18th Edition Compliant Consumer Unit

RutlandFox · Feb 24, 2019

Hello all.

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

eg Hager VML716RKO

Many thanks (Newbie)

SparkyChick · Feb 24, 2019

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 · Feb 24, 2019

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 · Feb 24, 2019

Yes.

Short answer

telectrix · Feb 24, 2019

littlespark said:
Yes.

Short answer

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

Andy78 · Feb 24, 2019

telectrix said:
and the long answer is.......... ?

.......Possibly

Cid · Feb 24, 2019

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 · Feb 24, 2019

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

spark 68 · Feb 24, 2019

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 · Feb 24, 2019

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 · Feb 24, 2019

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 · Feb 24, 2019

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 · Feb 24, 2019

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 · Feb 24, 2019

mattg4321 said:
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 · Feb 24, 2019

spark 68 said:
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.

[ElectriciansForums.net] 18th Edition Compliant Consumer Unit

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.