Low Ze, high(ish) R1+R2, Got a plan but just had an idea

[Mattja]

Hi all, thanks for replies!

Solution I'm going with is the 10kA Type B's.

1 question remains: Has anyone here worked with Cudis CUs before? Are they any good or are they a pile of crap?

I could go with Hager or Wylex for 10kA Type B RCBOs but this Cudis brand I've just spotted have the right devices going a lot cheaper. In total I'd be saving about £200-300 (even by central London prices that's a fair bit).

(18 circuits total currently, however one is feeding only a single fused spur unit that is both redundant - used to be for conservatory heaters - and mostly behind a plumbed radiator so that's coming out... I swear the next time I see a plumber I'm going to grin manically at him while stroking an electric-radiator)

 

[Mattja]

It appears all considerations here are for LE faults of which an rcd can provide protection for. What is the line impedance/short circuit current, has that been considered also?

Same reading, should've made clear my bad. It's a PME with Board right next to main fuse & meter.

 

[Octopus]

Hi all, thanks for replies!

Solution I'm going with is the 10kA Type B's.

1 question remains: Has anyone here worked with Cudis CUs before? Are they any good or are they a pile of crap?

I could go with Hager or Wylex for 10kA Type B RCBOs but this Cudis brand I've just spotted have the right devices going a lot cheaper. In total I'd be saving about £200-300 (even by central London prices that's a fair bit).

(18 circuits total currently, however one is feeding only a single fused spur unit that is both redundant - used to be for conservatory heaters - and mostly behind a plumbed radiator so that's coming out... I swear the next time I see a plumber I'm going to grin manically at him while stroking an electric-radiator)

Mixing brands of parts in Cu's isn't a good idea and come the 18th it isn't allowed at all

Why not fit a 20A?

 

[Mattja]

Hi Murdoch, reason for not going with a 20A is simply since I can keep it on a 32A so long as I get a device with 10kA breaking capacity (I'd totally forgotten last night that Type B's could be found with 10kA instead of 6kA BC).

I've no intention of mixing parts, it's going to be a board change (reasoning below) so I've got the choice of which brand to go with, and I've not used Cudis before but their 10kA type B RCBOs are a lot cheaper than other brands, so I'm tempted but slightly suspicious.

Currently there are no RCDs/RCBOs at all, except one in an outside socket. It's also a plastic CU located in the basement, right above it is the front door/bottom of the stairs. Customer has asked that I test and inspect and carry out works as I judge appropriate to make the installation safe and functional.

I'd take no issue with an existing plastic CU in a garage to the side of the house, or some other out-of-the-way location, but I don't think leaving the plastic CU in place below the bottom of the stairs and front door is appropriate since if there were a fire there it could quickly cut off the only way out (if you took up the floorboards between the stairs and front door and made a hole in the basement ceiling below that you'd see the CU below).

Also it's currently an MK, and they don't seem to do 10kA Type B RCBOs, so even if I were to just change devices inside it to have a 10kA breaking capacity I'd be back to needing Type Cs. As mentioned previously there's not room to put in RCDs, unless I use just 2 RCDs but it's a lot of circuits for that in my opinion (17, plus 1 more which may go back into use if they want to make use of that point in the conservatory again).

So what I believe is the best course of action is changing the CU, and putting in all 10kA type B RCBOs. Yes that's not cheap, but it's a very nice house in central London so that's fine. Reason I'm wondering about this Cudis brand is because £200-300 is still a fair bit of money to save if the product is up to scratch.

 

[Octopus]

Hi Murdoch, reason for not going with a 20A is simply since I can keep it on a 32A so long as I get a device with 10kA breaking capacity (I'd totally forgotten last night that Type B's could be found with 10kA instead of 6kA BC)..

Why do you think a 32A is required - is it a kitchen?

 

[Toneyz]

Only skimmed this but why do you want to fit a C rather than a B when I did domestic all we ever fitted was B and had no callbacks the only time it tripped out was when site workers plugged their transformers in.

 

[Mattja]

It's not the kitchen, it's the first floor. There are 2 rooms that I expect to be used as bedrooms, a bathroom in between them with fused spur for electric towel rails, 1 large room at the front that I'd expect to be a living room or some such thing, and the hallway. Windows are rather large though so I wouldn't be surprised if they get a few electric heaters out in the winter. Being a large house with at least 4 bedrooms (assuming that large room on 1st floor isn't used as a 5th bedroom) that's going to be rented out I wouldn't be surprised if someone had a kettle/microwave on that floor.

So yes 20A may be just fine. But it's not implausible in my mind that they may draw over 20A briefly in the winter from heating appliances and maybe a vacuum thrown in.

 

[Mattja]

Only skimmed this but why do you want to fit a C rather than a B when I did domestic all we ever fitted was B and had no callbacks the only time it tripped out was when site workers plugged their transformers in.

Because I'd forgotten (being tired last night) that I could get type B with 10kA breaking capacity instead of 6kA.

 

[Nigel]

Can someone explain to me when BS60898 MCBs started to have different maz Zs permitted based on of they were 6ka or 10ka?

 

[westward10]

This is definitely being over thought.

 

[Nigel]

This is definitely being over thought.

And when did ka come into it and what does that have to do with this job?

A bit of blind leading the blind going on here.

 

[Mattja]

Essex, on a 32A Type C max Zs permitted is 0.54. So if I had to use a Type C I'd have to go down to 20A, for which the max Zs permitted is 0.87 (circuit has Zs = 0.7something).

Short circuit/earth fault current at origin of over 6kA due to low Ze/Zn or (w/e you call it, same reading on both) so I need 10kA breaking capacity, which I would get with Type Cs.

However since 10kA breaking capacity Type Bs exist, which I had forgotten last night, I can use those which means my max permitted Zs is 1.08 for a 32A breaker, so no need to bring it down.

Now since it's got to be RCBOs (in my opinion too many circuits to be sensible for 2 RCDs, and not enough space to put in a bigger board or 2 boards to allow for more), and since it's a plastic board in an unsuitable location, that leaves me with 1 reasonable course of action:
New consumer unit, filled with Type B RCBOs at 10kA breaking capacity.

The only question left if the brand. Currently options I'm looking at are Hager, Wylex and Cudis.
Hager I'm not a fan of (only put in one of those and those stupid rectangular knockouts put me right off).
Wylex I prefer anyway and I can get the RCBOs about £100 cheaper (in total, 17 circuits).
Cudis I've never used before, but the RCBOs for them would be about £300 cheaper than Hager or £200 cheaper than Wylex, but I'm not sure I trust them since I've not used them before.

So, are Cudis any good?

EDIT: Cudis* not Cubis

 

[Octopus]

So yes 20A may be just fine.

That's the solution then.

 

[Strima]

I'm still confused as to why the OCPD breaking capacity has an impact on what curve to use?

 

[Nigel]

Essex, on a 32A Type C max Zs permitted is 0.54. So if I had to use a Type C I'd have to go down to 20A, for which the max Zs permitted is 0.87 (circuit has Zs = 0.7something).

Short circuit/earth fault current at origin of over 6kA due to low Ze/Zn or (w/e you call it, same reading on both) so I need 10kA breaking capacity, which I would get with Type Cs.

However since 10kA breaking capacity Type Bs exist, which I had forgotten last night, I can use those which means my max permitted Zs is 1.08 for a 32A breaker, so no need to bring it down.

Now since it's got to be RCBOs (in my opinion too many circuits to be sensible for 2 RCDs, and not enough space to put in a bigger board or 2 boards to allow for more), and since it's a plastic board in an unsuitable location, that leaves me with 1 reasonable course of action:
New consumer unit, filled with Type B RCBOs at 10kA breaking capacity.

The only question left if the brand. Currently options I'm looking at are Hager, Wylex and Cudis.
Hager I'm not a fan of (only put in one of those and those stupid rectangular knockouts put me right off).
Wylex I prefer anyway and I can get the RCBOs about £100 cheaper (in total, 17 circuits).
Cudis I've never used before, but the RCBOs for them would be about £300 cheaper than Hager or £200 cheaper than Wylex, but I'm not sure I trust them since I've not used them before.

So, are Cudis any good?

EDIT: Cudis* not Cubis

Your opening posts bears no resemblance to this post.

Next time try and think more about the detail you post and the terminology you use. It is important and you have wasted people’s time.

 

[Nigel]

I'm still confused as to why the OCPD breaking capacity has an impact on what curve to use?

It doesn’t as you know. The op has had us up a garden path talking about Zs when he should have been asking about PFC.

 

[Strima]

It doesn’t as you know. The op has had us up a garden path talking about Zs when he should have been asking about PFC.

Nothing like a good thread on a Sunday to clear your head...

 

[Toneyz]

What work are you undertaking?
What is the existing board?

 

[Toneyz]

So is the choice for 10KA MCB's is PFC being above 6KA based upon 230v /0.03?

 

[Strima]

What's your measured PFC?