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?

 

[pc1966]

In terms of the rack, even if you just plan on plugging it in to a 13A socket then better to have a single point (single or double socket, 16A/20A) radial just for it.

That way you don't have to deal with leakage on other circuits contributing to any nuisance tripping of the supply, and if it proves to be trip-happy due to the accumulation of all stuff in the rack, you know that is the reason.

 

[j0hnnn]

In terms of the rack, even if you just plan on plugging it in to a 13A socket then better to have a single point (single or double socket, 16A/20A) radial just for it.

Yea, agreed, this was the whole reason behind this installation, to get the rack on its own circuit. Any issue making this a 32A circuit?

I'm going to start reeling it back on the AFDDs though, maybe have this new circuit, shower and garage with them and rest on RCBOs. Although, as I mentioned previously, Hager RCBOs are single pole so I might have to just settle for another brand that the electrician will recommend.

 

[littlespark]

Approach a few electricians and get more than one quote. Make sure they understand you want extra space for future works.

Don’t go for the first name that appears on mybuilder or checkatrade…. In fact… steer clear.

Best option is word of mouth recommendations from friends and neighbours.

 

[pc1966]

Yea, agreed, this was the whole reason behind this installation, to get the rack on its own circuit. Any issue making this a 32A circuit?

Easy to do, just heavier cable, etc. But why?

• If it is a single 13A socket then 13A is max.
• If double then typically they are rated at 20A between the two.
• If you are actually using much more than 13A on your IT kit you will have both an eye-watering electricity bill, and a need for A/C to keep the area cool.

I'm going to start reeling it back on the AFDDs though, maybe have this new circuit, shower and garage with them and rest on RCBOs. Although, as I mentioned previously, Hager RCBOs are single pole so I might have to just settle for another brand that the electrician will recommend.

While you get AFDD in all sorts of ratings, for now the main push has been to have them on socket outlet circuits, presumably because of more risk from arcing from damaged cables / plugs / etc. Inspecting and testing your appliances ("PAT testing") might give you better prevention for the money.

Anecdotally the higher risk of overheating has been high power circuits like cookers & showers that were badly installed so terminals incorrectly tightened and/or poor quality or inappropriate parts used. Often they don't arc as it is basically just a high resistance contact.

RCD/RCBO provide a lot of the protection for general cable damage due to rodents, crushing, nailing, etc., that could cause a fault that creates heat but is not "hard" enough to trip the over-current protection, and so go some way towards reducing the fire risk anyway. With RCBO you find our which circuit is faulted quickly, and don't get healthy ones tripping as well. Also less risk of nuisance tripping as less accumulation of leakage as less appliances per circuit.

Finally, I guess you have a good interlinked smoke alarm system (like Aico, etc)? That is probably a far more important safety aspect then AFDD versus RCBO!

 

[pc1966]

Best option is word of mouth recommendations from friends and neighbours.

The OP might find someone on here that is close enough and already knows the discussion. Some general location like town or (part) postcode (not actually address) would help!

 

[j0hnnn]

If you are actually using much more than 13A on your IT kit you will have both an eye-watering electricity bill, and a need for A/C to keep the area cool.

Yea, true, I figured if I'm getting a new circuit, why not just do 32A in case it gets repurposed later but there is still going to be the existing ring so 20A for a double socket should more than suffice.

Finally, I guess you have a good interlinked smoke alarm system (like Aico, etc)? That is probably a far more important safety aspect then AFDD versus RCBO!

Of course, using (unfortunately) FireAngel Pro Connected and tested regularly. Interestingly and somewhat related to this thread, when I first moved into this home, I wanted to install Aico products but was told this was excessive and FireAngel would be fine so I took the advice. Lessons learned and here we are.

The OP might find someone on here that is close enough and already knows the discussion. Some general location like town or (part) postcode (not actually address) would help!

I actually know a few local people that have done work for friends and family that come recommended so will be able to discuss this installation with them. I just didn't want to approach them initially because as someone said on this thread, they don't really want to get into discussions and are busy as it is.

 

[nicebutdim]

Of course, using (unfortunately) FireAngel Pro Connected and tested regularly. Interestingly and somewhat related to this thread, when I first moved into this home, I wanted to install Aico products but was told this was excessive and FireAngel would be fine so I took the advice. Lessons learned and here we are.

One expensive option that few here would talk anyone out of.

 

[pc1966]

Yea, true, I figured if I'm getting a new circuit, why not just do 32A in case it gets repurposed later but there is still going to be the existing ring so 20A for a double socket should more than suffice.

20A for general purpose sockets is usually considered adequate for 50 m^2 of area so even on its own it could be extended to other outlets up there.

For 32A then (from memory) a radial circuit for 75m^2 and RFC for 100m^2, with the difference down to the acceptable cable lengths at sane cable sizes for voltage drop, as much as anything else.

 

[j0hnnn]

Thanks! So what would be my other high quality/reliable options if I were to just stick to RCBOs and given that Hager ones are single pole?

 

[westward10]

It isn't relevant they are single pole.

 

[davesparks]

Thanks! So what would be my other high quality/reliable options if I were to just stick to RCBOs and given that Hager ones are single pole?

Personally I have used contactum for domestic work since I was an apprentice and have not had any major issues with them.


Is there a particular reason you need double pole protection? There's not normally any need for it in the average UK installation.

 

[pc1966]

Thanks! So what would be my other high quality/reliable options if I were to just stick to RCBOs and given that Hager ones are single pole?

For most purposes the single pole switching RCBO are fine, it is only specific cases like EV charges that need double pole and for that you can fit a MCB and separate RCD.

You mentioned a lack of space, some (like Hager) do double-row CU enclosures and that might help if you are short of width but have height to spare.

Personally I would go with the main stream brands (Hager, Schneider, Wylex, Crabtree, etc) and avoid the own-brand ones (Proteus, Axiom, etc).

 

[j0hnnn]

Is there a particular reason you need double pole protection?

Ahh, there is a couple of posts earlier on in this thread where people recommended getting double pole so was just trying to follow the advice.

For most purposes the single pole switching RCBO are fine, it is only specific cases like EV charges that need double pole and for that you can fit a MCB and separate RCD.

I have plans to install an EV charger at some point in the future, in this case, what you suggest makes sense but could also save a module space here and go with their AFDD as it's already DP?

You mentioned a lack of space, some (like Hager) do double-row CU enclosures and that might help if you are short of width but have height to spare.

Good point! I saw the Hager double-row CU but didn't think much of it. These might make things less of a hassle to install given the space.

Personally I would go with the main stream brands (Hager, Schneider, Wylex, Crabtree, etc) and avoid the own-brand ones (Proteus, Axiom, etc).

Definitely, I'm happy to pay a bit extra for main stream brands with higher quality hence why I want to make sure if I'm getting the work done, the electrician is not just using any random brand.

 

[timhoward]

Is there a particular reason you need double pole protection? There's not normally any need for it in the average UK installation.

Ahh, there is a couple of posts earlier on in this thread where people recommended getting double pole so was just trying to follow the advice.

Single Pole, Single Pole Switched Neutral, and Double Pole are all different things. Hager RCBO's are Single Pole.
I was recommending Single Pole Switched Neutral as I favour devices the isolate the N. It makes it possible to ‘contain’ neutral-earth faults and any future diagnostics are so much easier.

Regarding choice, you need to talk to your electrician as different sparks have accounts at different wholesalers and can get different brands at good prices. We all have things we are used to and prefer to fit too.