18th Edition Compliant Consumer Unit

[RutlandFox]

Hello all.

Quick question: Are 17th reg 3rd amendment metal consumer units compliant with 18th edition regs?

eg Hager VML716RKO

Many thanks (Newbie)

 

[SparkyChick]

I believe the 18th edition requires the RCDs to be rated such that they cannot be subjected to overload. What this means is that if the DNO fuse is 80A, both RCDs must be rated at 80A, 100A DNO fuse = 100A RCDs.

There has been some debate about this in this thread:-

RCD RATING VS. SERVICE FUSE RATING - https://www.electriciansforums.co.uk/threads/rcd-rating-vs-service-fuse-rating.171274/

 

[SparkyChick]

And of course, don't forget you may need to accommodate SPDs and if the client goes for them... AFDDs (which may mean using two boards instead of one )

 

[littlespark]

Yes.

Short answer

 

[telectrix]

Yes.

Short answer

and the long answer is.......... ?

 

[Andy78]

and the long answer is.......... ?

.......Possibly

 

[Cid]

In a nutshell, if you have 100amp cut out and 63amp rccb - don't overload it with mcbs that exceed the sum of 63amps. Use rcbos for the big circuits.

 

[Deleted member 26818]

Is it just Tool Station selling off 17th edition CUs cheap?

 

[spark 68]

If you look at the thread SC referred to above ^^^^ and read that reg (536.4.202) properly it is the design current for that RCD that needs to comply not the size of the company fuse etc, etc, , the last paragraph of that reg states manufacturers instructions should be followed, however in the same regs book, or at least in the 17th amd 3 book only states that manufacturers instructions should be taken account of.

 

[Zdb]

Probably best to supply full RCBO boards (with SPD) unless you can guarantee that your RCDs will be subjected to less than 9mA of earth leakage.

 

[spark 68]

Unlikely to hit 9mA in a domestic environment, besides which if you hit 10mA on a given circuit you are then into HI earthing, we hit this on office installs quite frequently where a lot of computers are installed.

Edit: 30mA RCDs tend not to trip until circa 22mA mark, @ 15mA they should not trip either.

 

[mattg4321]

Seen the price of the 100A RCCB's!

Doubles the price of most consumer units. Bet we won't be seeing many of them being fitted. Are they actually needed? Seems like the manufacturers trying to pull a fast one to me.

 

[spark 68]

Read Reg 536.4.202 again, and you will see it is the design current Ib that needs to be complied with, which is what most of us have always done anyway.
As said manufacturers instructions should be taken account of, not followed blindly.

Ps. Spin London was correct too it is also the ICn that is also important,

 

[Octopus]

Seems like the manufacturers trying to pull a fast one to me.

Hit, nail and head...........

If anybody thinks that they need to make sure that each RCD value is equal to or less than the main fuse they are being mislead.

Take this another step and you shouldn't have the sum of the MCB's or RCBO's exceeding the DNO fuse ............. which is madness.

 

[Zdb]

Unlikely to hit 9mA in a domestic environment, besides which if you hit 10mA on a given circuit you are then into HI earthing, we hit this on office installs quite frequently where a lot of computers are installed.

Edit: 30mA RCDs tend not to trip until circa 22mA mark, @ 15mA they should not trip either.

TBH I'm not sure what the average leakage per RCD is for a typical split load domestic board as I don't do a lot of domestic. I would still recommend full RCBO though for a number of reasons.

 

[spark 68]

Oh I don't disagree, a full RCBO board is always nice to have if the customer will go for it, however they should always have been DP, or at least SPSN from the get go for obvious reasons.

 

[Toneyz]

I understand that Hager is going to install 100A as standard in the split boards you watch the assessors pulling us up on it.

 

[Ian1981]

Historically we have used diversity of the final circuits to ensure that the rccb is not overloaded.
Now it seems we can not rely solely upon diversity of the final circuits downstream of the rccb and overload protection must be ensured by other means like having the upfront ocpd rated lower or equal to the rccb and main switch or ensure that the final circuits added are not greater than the rccb and ensuing manufacturers instructions are complied with.
I know with Hager they have taken the approach of fitting 2x 100amp rccb’s (Also now type A) in their dual rcd consumer units so obviously they intend to ensure that their rccb’s are not overloaded and have defaulted to use 100amp devices.
This is certainly the guidance also given by my companies scheme provider.

 

[spark 68]

Which reg states that though Ian ? 536.4.202 doesn't as far as I read it, Hagar is only one manufacturer out of many.
I normally take what you have to say seriously as you are one of the few that happens to know what you are talking about.

I had a look at the corrigendum for the 18th (yes mistakes again!) and nothing was mentioned wrt to this.

 

[Wilko]

I think it's the last para of that reg that's the killer, where they state " OCPD rating shall be selected in accord with manufacturer's instructions" . Rightly or wrongly, Hager has jumped in with both feet.