Sanity check on plan for CU replacement (MCB to RCBO AFDD)

[j0hnnn]

I'm planning a replacement for my existing domestic CU and would like to have it sanity checked before I get an electrician involved. The main reason for replacing the whole CU is that I would like to have an additional circuit to the attic which would be isolated from the existing one. Long story short, I've got a server rack up there which is increasing in power consumption and had a trip when a computer on the same circuit got powered on. Second reason is that the current CU is using MCBs and also there is no more space left. Instead of planning for another smaller CU, I want to get this done properly and modernised.

Existing Setup

The existing CU is 14-way (all used up). The main fuse from the supplier is 60A.

• CPN IS2100 Isolater Switch (100A) - 100A, 2 Pole. | CPN Cudis - https://cudis.co.uk/product/100a-2-pole/
• 3x CPN MC110B MCB (10A) - 10A - B Curve | CPN Cudis - https://cudis.co.uk/product/10a-b-curve/
• 3x CPN MC116B MCB (16A) - 16A - B Curve | CPN Cudis - https://cudis.co.uk/product/16a-b-curve/
• 4x CPN MC132B MCB (32A) - 32A - B Curve | CPN Cudis - https://cudis.co.uk/product/32a-b-curve/
• 1x CPN RC263/030 RCD (63A) - 63A 30mA Type B | CPN Cudis - https://cudis.co.uk/product/63a-30ma-type-b/

Upgrade Plan

I have spent the last few weeks researching everything electrical related to CUs and tried to incorporate as much of the recommendations I have read online. Since I'm not an electrician, the following is likely to not make sense, completely wrong or "overkill", hence me seeking advice. I fully understand that this plan may require rewiring and won't be cheap so money isn't going to be the significant deciding factor here.

Having looked into the different brands, I'm have made the decision to go with Hager. As mentioned previously, my immediate requirement is to have a new circuit to the attic but would be looking to have an EV charging point installed in the future. So my thought is to get the main supplier fuse upgraded. If I'm reading correctly, going form 60A to 80A could be simple but going to 100A would require a service head replacement. Also, if the cabling into the home isn't adequate, there will be extra work involved. Ideally, I get the main supplier fuse upgraded from 60A to 100A giving me more flexibility for the future. I want to get an isolation switch installed at the same time as there currently isn't one between meter and the CU. I guess I just need to get in touch with my DNO to see what they can do and whether the tails need upgrading too.

For the new CU, I'm considering the following:

• Hager VM120K CU Enclosure (20-way) - VM120K | Hager UK - https://hager.com/uk/products/h/vm120k-conunitd3020w100asw-discknockouts
• Hager VME02SPD SPD Type 2 - VME02SPD | Hager UK - https://hager.com/uk/products/h/vme02spd-cu-surge-protection-kit-type-2
• Various RCBO AFDDs:
  • Hager ARR910U (10A) - ARR910U | Hager UK - https://hager.com/uk/products/h/arr910u-rcbo-with-arc-detect1m-10a-b-6ka-a-30ma
  • Hager ARR916U (16A) - ARR916U | Hager UK - https://hager.com/uk/products/h/arr916u-rcbo-with-arc-detect1m-16a-b-6ka-a-30ma
  • Hager ARR932U (32A) - ARR932U | Hager UK - https://hager.com/uk/products/h/arr932u-rcbo-with-arc-detect1m-32a-b-6ka-a-30ma

With this in place, I'm hoping to have a second circuit installed in the attic purely for the server rack. Currently it's powered using a single socket to a 13A PDU. Maybe I can separate the load here across two PDUs plugged into two different 13A fused sockets from the new circuit, at least I should have more options. I've looked into commando sockets but like I said, unlikely I'll have a load that would warrant it.

So, how does this all sound?

 

[MJPD29]

The price of this to buy without labour is going to be eye watering. There is currently no requirement to have afdd protection for circuits in your house, it is only a recommendation for socket circuits, but not mandatory.

 

[nicebutdim]

There's nothing obvious that stands out as being problematic in your plan, but it might be best to put it to an electrician who would be able to advise on your plan in relation to specifics of the installation.

I'm sure you have good reasons for choice of circuit protection, but they aren't obvious to me and, again, something which should be discussed with whoever will carry out the work.

 

[SJD]

Re the enclosure, Hager units typically come with the option of round or rectangular knockouts top & bottom, check which would be more convenient, the part numbers are slightly different (e.g. K vs RK) to select which option.

Typically you'd buy the enclosure with the SPD already fitted, which would be cheaper than buying them separately. Again, gets specified in the part number (e.g. with an SPD suffix).

I installed a consumer unit with a selection of Hager AFDDs recently (care home). The AFDDs were quite expensive, circa £100 each. As just mentioned, it is only a recommendation (assuming you are not a care home), and unless money really is no object, I'd consider if you really need them all. The Hager AFDDs can be connected to from a phone/laptop etc via Bluetooth, and you can download the last 16 (I think) trips, with data like what type of trip, how long the circuit was up. But I found the software a bit clunky and immature to use and did not work quite as described, though I did manage to connect and see this data. You can upload new firmware to the AFDDs if needed.

That said, the reason I chose Hager over my usual brand (Fusebox) is the expectation that Hager would more likely to still be around in 10 or 20 years for spares.

 

[j0hnnn]

The price of this to buy without labour is going to be eye watering. There is currently no requirement to have afdd protection for circuits in your house, it is only a recommendation for socket circuits, but not mandatory.

Yea, it's not going to be cheap. If I do all the breakers (11) as the AFDD type, it comes to around £1100 just for those. As an alternative, I could just do the lights circuits on their standard RCBOs (ADA310G | Hager UK - https://hager.com/uk/products/h/ada310g-rcbo-1p-6ka-b-10a-30ma-type-a-1m) and rest AFDD variant.

I'm sure you have good reasons for choice of circuit protection, but they aren't obvious to me

Just thinking that if money wasn't a significant factor, am I better off just following recommendations albeit not being mandatory - yet?

Re the enclosure, Hager units typically come with the option of round or rectangular knockouts top & bottom, check which would be more convenient, the part numbers are slightly different (e.g. K vs RK) to select which option.

Thanks, I was actually trying to figure out the difference between VM120 and VM120K, this cleared it up (hopefully the electrician would know about this).

Typically you'd buy the enclosure with the SPD already fitted, which would be cheaper than buying them separately. Again, gets specified in the part number (e.g. with an SPD suffix).

I saw a few with SPD options but wasn't sure if the SPD provided is the same type or lower quality. I initially looked at Type 1 + 2 SPD but this wasn't available in the SPD suffixed part numbers so ended up with Type 2. I should probably consider the ones with SPD fitted if it's the same one they are selling individually.

As just mentioned, it is only a recommendation (assuming you are not a care home), and unless money really is no object, I'd consider if you really need them all. The Hager AFDDs can be connected to from a phone/laptop etc via Bluetooth

I most likely don't need them all to be AFDD, considering now as per pervious message just to do sockets and anything high current to use them instead. I saw the Bluetooth connectivity and the app and did read about some hoops you have to jump through during FW upgrades but alas, it's a nice to have and wouldn't have much bearing on the decision making.

 

[nicebutdim]

Yea, it's not going to be cheap. If I do all the breakers (11) as the AFDD type, it comes to around £1100 just for those. As an alternative, I could just do the lights circuits on their standard RCBOs (ADA310G | Hager UK - https://hager.com/uk/products/h/ada310g-rcbo-1p-6ka-b-10a-30ma-type-a-1m) and rest AFDD variant.


Just thinking that if money wasn't a significant factor, am I better off just following recommendations albeit not being mandatory - yet?

There's no reason not to fit AFDDs, but is there any benefit in doing so? Is the property used for commercial purposes?

I saw a few with SPD options but wasn't sure if the SPD provided is the same type or lower quality. I initially looked at Type 1 + 2 SPD but this wasn't available in the SPD suffixed part numbers so ended up with Type 2. I should probably consider the ones with SPD fitted if it's the same one they are selling individually.

What is the earthing arrangement at the property? Buying what you think is best might be an ultimately pointless exercise. This ties in with my suggestion to engage the services of an electrician, rather than compile a shopping list on the basis of information gathered from various parts of the internet. Regardless of how good a source might be, they won't reimburse you for items bought that don't meet the requirements of your installation.

 

[davesparks]

It is good that you have read up on this and familiarised yourself with the options, but I'd suggest you don't fix on a particular manufacturer or specific arrangement until you've spoken to the electricians who will be quoting the job.

We all work slightly differently and have our preferred manufacturers so get a few quotes from a few electricians and see what they say.

As far as AFDDs go you have obviously researched them and have decided you'd like to add this type of protection, so if the price is not an issue for you then go ahead with it.
Just be aware that they are a relatively new technology and any tripping problems will take a bit longer to diagnose as we just don't have the years of experience we have about other faults and tripping problems.

 

[pc1966]

I would add that if you have reason to want the AFDD added arc-fult protection then Hager are a good choice as they support bluetooth diagnostics and the ability to update firmware. I'm not sure anyone else does that.

As @davesparks says many sparkys have favourite brands so might want to offer others, but if you are looking for high quality then Hager and Schneider are your best bets if affordable.

 

[nicebutdim]

I would add that if you have reason to want the AFDD added arc-fult protection then Hager are a good choice as they support bluetooth diagnostics and the ability to update firmware. I'm not sure anyone else does that.

As @davesparks says many sparkys have favourite brands so might want to offer others, but if you are looking for high quality then Hager and Schneider are your best bets if affordable.

If this premises is domestic I'd add Crabtree starbreaker to the list, for ease of future additions. Although no Bluetooth connectivity would be possible.

 

[pc1966]

If this premises is domestic I'd add Crabtree starbreaker to the list, for ease of future additions. Although no Bluetooth connectivity would be possible.

The Crabtree Starbreaker are nice, innards same as Wylex, and one of the original single-module AFDD. As for the RCBO they have the nice feature of neutral-switching.

 

[nicebutdim]

The Crabtree Starbreaker are nice, innards same as Wylex, and one of the original single-module AFDD. As for the RCBO they have the nice feature of neutral-switching.

And that lovely plug in live busbar.

 

[j0hnnn]

There's no reason not to fit AFDDs, but is there any benefit in doing so? Is the property used for commercial purposes?

It's a domestic property and not used for any commercial purposes. Aside from the inherit benefits from detecting arc faults, my thinking is that if a situation would arise, I'd be some what protected. Although it's not mandated for domestic installations, I'm going by the fact that if it's mandated for premises with sleeping accommodation, it must/should be good for domestic too. Also, if I'm replacing the MCBs and I have the option to go for RCBOs or RCBOs with AFDD, if money isn't a big factor, would you still settle just for RCBOs?

What is the earthing arrangement at the property? Buying what you think is best might be an ultimately pointless exercise. This ties in with my suggestion to engage the services of an electrician, rather than compile a shopping list on the basis of information gathered from various parts of the internet. Regardless of how good a source might be, they won't reimburse you for items bought that don't meet the requirements of your installation.

Standard earthing setup with bonding to gas and water pipes. I will definitely be engaging with an electrician but I wanted to get a feel for what I'm planning makes sense. I know there will be a lot of factors that will come into play on the actual installation but I wanted to have some understanding of all this before I blindly go and ask someone to do it. This is why I spent my time researching and hopefully the information I have presented is sane. I was hoping the collective feedback of many would be better at this stage than approaching an electrician locally. If everyone were to post saying this wouldn't be up to code or it's unsafe then at least I know I'm completely off track.

It is good that you have read up on this and familiarised yourself with the options, but I'd suggest you don't fix on a particular manufacturer or specific arrangement until you've spoken to the electricians who will be quoting the job.

The reason I've picked this particular manufacture is because I've spent that past few weeks looking into various manufacturers and I wanted to make sure I'm getting quality rather than going for cheaper options. I don't have an issue spending a bit more if I know the product is good and this is the impression I got with Hager on most posts/reviews. The specific arrangement was just put up for discussion as a first pass with the members of this forum before I go ahead and speak to electricians.

As @davesparks says many sparkys have favourite brands so might want to offer others, but if you are looking for high quality then Hager and Schneider are your best bets if affordable.

Totally understand that some will have brand loyalty. I'll just need to find someone that has a similar alignment to a brand I'm considering. If others posted saying Hager isn't a good choice then I would know not to be picky and let the electrician advice me on their preference but that's not the case, as you say, Hager is one of the higher quality brands and I'm leaning towards quality over value here.

For the electricians on the forum, if someone approached you with a similar request to mine, how would you feel and deal with the situation? I understand that it could come off as trying to tell one how to do their job but I'm hoping I've got some valid requests/thoughts for discussion/advice in there albeit being excessive? As I said before, I wanted to post here to get feedback from a larger pool of electricians first.

 

[nicebutdim]

It's a domestic property and not used for any commercial purposes. Aside from the inherit benefits from detecting arc faults, my thinking is that if a situation would arise, I'd be some what protected.

You would be afforded protection against certain types of earth fault, but not all.

Some protection would be better than none, should such a fault occur.

Although it's not mandated for domestic installations, I'm going by the fact that if it's mandated for premises with sleeping accommodation, it must/should be good for domestic too.
Also, if I'm replacing the MCBs and I have the option to go for RCBOs or RCBOs with AFDD, if money isn't a big factor, would you still settle just for RCBOs?

I'd consider the question on its respective merits for each individual installation. Arc fault protection is relatively new technology where UK electrical installations are concerned.

It has been used quite widely in US domestic installations for a longer period of time and opinions about its benefit are mixed over there, although negative opinions may stem from the sort of installation which might benefit most from atc fault protection.

Standard earthing setup with bonding to gas and water pipes. I will definitely be engaging with an electrician but I wanted to get a feel for what I'm planning makes sense. I know there will be a lot of factors that will come into play on the actual installation but I wanted to have some understanding of all this before I blindly go and ask someone to do it. This is why I spent my time researching and hopefully the information I have presented is sane. I was hoping the collective feedback of many would be better at this stage than approaching an electrician locally. If everyone were to post saying this wouldn't be up to code or it's unsafe then at least I know I'm completely off track.

This doesn't address the question I raised about earthing, but that won't be an issue if you intend bringing an electrician on board before buying materials.

As per my initial post; there's nothing flawed in your plan, although it does appear to be more risk averse than many would consider necessary.

Chances are we'll see boards filled with AFDDs in the not too distant future, but I'd expect they'll be considerably less expensive by then and possibly more refined. With brands like Hager or Crabtree, it's very likely that availability won't be an issue in the future as both have a great track record where backward compatibility is concerned.

The bare bones of your plan is sound, if excessive, and specific details can be ironed out when an electrician looks at the installation.

They may not bat an eyelid at your proposals, but nor should they have any issue fitting what might be considered an overly expensive option if you explain that it's what you want.

 

[Risteard]

The Crabtree Starbreaker are nice, innards same as Wylex, and one of the original single-module AFDD. As for the RCBO they have the nice feature of neutral-switching.

This (i.e. switching all live conductors) will be essential for adding an EVSE installation to this new DB later as stated.

 

[littlespark]

An earlier point raised. A 60, 80 and 100A main fuse all use the same fuse holder, so you may not meet a new head. (Although, you do imply money isn’t a problem)

The problem with upsizing the fuse is whether it would still offer protection to the supply cable coming into the property. (Very likely anyway)

 

[pc1966]

Long story short, I've got a server rack up there which is increasing in power consumption and had a trip when a computer on the same circuit got powered on.

How big are you planning this rack to be?

Are you using a UPS on this?

Generally computer racks can be quite leaky, more than the ~9mA max recommended for your usual 30mA additional protection RCD/RCBO used for general circuits.

If that is the case then hard-wiring the UPS supply without RCD on its input using a suitably protected cable like SWA to a FCU or similar, possibly with supplementary bonding to the rack, would be a better idea. Any RCD protection on sockets fed from the UPS ought to be on its output, say via an RCD FCU (or two, if splitting a lot of low power but leaky loads) to some block(s) of 13A or 10A IEC outlets..

Disconnecting the input to a UPS does nothing to protect some poor sod on its output!

 

[plugsandsparks]

To answer the Ops question - how would an electrician react to the home owner specifying the Cu design ?
TBH - it has never happened, lol
There is no brand loyalty, as such, it is just some brands have quirks in their products that grind your gears when you have to deal with them. I tend to settle on a brand that is supported by local wholesaler, a brand that does not have a key part in short supply, a brand whose quality of housing and fasteners is dependable and strong. Lastly a brand that supports options i may need, its very different in the commercial world, so i tend to be more brand conscious in commercial and industrial. Domestic, you have slightly different priorities.

I think the question may be more relevant to ask yourself how you are likely to react when the electrician proposes a different solution which you have spent hours of research on. Dont expect an electrician to engage in a lengthy conversation, we are not research bods, we are a trade with years of experience in both installations and fault finding / maintenance, this all comes into play when designing any solution.

E.g. I would recommend to get a quote for your installation upgraded to 100A , you may be lucky. A good strong CU housing, the bigger the better, over-size it by at least 20% from what you know today. All RCBO with DP switching, earthing system checked for best possible ZE. SPDs - cheap enough but need to be checked regularly, AFDDs if you really want them but i personally am in no rush to fit them in my own home, could be useful for an electric shower cct, car charger cct or any long duration high power loads.

 

[timhoward]

Also, if I'm replacing the MCBs and I have the option to go for RCBOs or RCBOs with AFDD, if money isn't a big factor, would you still settle just for RCBOs?

I've read this quite quickly, but I'll throw in that while Hager are excellent, unlike other brands their RCBO's only switch the live, not the neutral.
(Also beware that CEF say Hager Single Pole and Neutral, but they aren't, as the photo shows )

So I'd rather have the highly expensive Hager AFDDs or a lesser brand with RCBOs that switch both poles.

If it were me and I was splashing out I'd go the Crabtree route myself. I actually installed Fusebox in my own house but that is because no one was paying me to do it....and I think their perfectly adequate.

 

[j0hnnn]

Chances are we'll see boards filled with AFDDs in the not too distant future, but I'd expect they'll be considerably less expensive by then and possibly more refined. With brands like Hager or Crabtree, it's very likely that availability won't be an issue in the future as both have a great track record where backward compatibility is concerned.

That's a good point. It certainly feels risky opting for what's essentially a new product which most likely can be refined and be cheaper. Given all the feedback so far, I'm now on the fence of going all out AFDDs here, especially since this isn't going to be my final home.

How big are you planning this rack to be?

Are you using a UPS on this?

It's 20U, mostly networking gear with a few servers that could theoretically pull up to 700W individually but idle is around 100W and average during moderate use has been around 150W - 200W. So it's not really a that big considering how big and power hungry racks can be so I haven't planned in anything complex for power here other than the two PDUs (one IEC outlets and other standard UK). Up until recently, the PDUs came off the an APC UPS that had its battery fail so I'm still looking at options to replace that but on hold until I figure out what I'm going to do with the new CU/circuit. Currently, everything is powered off the mains socket. Nothing running is mission critical and everything is backed up (3-2-1) so I'm pondering whether I'll need a UPS again with proper protection in place.

E.g. I would recommend to get a quote for your installation upgraded to 100A , you may be lucky. A good strong CU housing, the bigger the better, over-size it by at least 20% from what you know today. All RCBO with DP switching, earthing system checked for best possible ZE. SPDs - cheap enough but need to be checked regularly, AFDDs if you really want them but i personally am in no rush to fit them in my own home, could be useful for an electric shower cct, car charger cct or any long duration high power loads.

Yea, hopefully going from 14 to 20 ways is enough for what I'll be needing as long as I'm in this house. Already struggling to find space where the existing CU is to replace with something bigger so will potentially need to a new mounting board above the current one, I'll leave this up to the electrician to figure out though. Are earthing system checks for ZE standard part of CU installs or is this something I would have to request the electrician carry out?

I've read this quite quickly, but I'll throw in that while Hager are excellent, unlike other brands their RCBO's only switch the live, not the neutral.
(Also beware that CEF say Hager Single Pole and Neutral, but they aren't, as the photo shows )

So I'd rather have the highly expensive Hager AFDDs or a lesser brand with RCBOs that switch both poles.

This is the unfortunate thing. I had this all planned out with AFDDs which are single module double pole and neutral. As you say, their RCBOs are not, although, their commercial breakers are DP (ADA932U | Hager UK - https://hager.com/uk/products/h/ada932u-rcbo-1pn-6kab-32a-30ma-a) but then at this point it's even more excessive, double module and I would be better off AFDDs with regards to protection and cost.

So, with all the feedback so far, it's clear this is a pretty excessive and an overly risk averse setup for what I'd consider is a "typical home" then I'm back to the drawing board again to consider what my options are for high quality DP RCBOs... Schneider? I've not really came across Crabtree but there seem to be a lot of positive chat about them in this thread so far.

 

[pc1966]

Are earthing system checks for ZE standard part of CU installs or is this something I would have to request the electrician carry out?

They should be. Checking the supply Earth nature & quality, and bonding of extraneous parts like service pipes, would be an essential aspect of any change to a CU, let along complete replacement.