consumer unit questions

[wannabesparky]

1. on a TT system do you still need 100ma on the new 17th edition consumer units
2. Do you still need a time delay rcd on a TT system with these new boards?
3. also, bear with me .... still learning ..... when you go to change a consumer unit how do you know which board to fit? sensible answers please.

many thanks

 

[piz]

1. on a TT system do you still need 100ma on the new 17th edition consumer units

No you dont

1. Do you still need a time delay rcd on a TT system with these new boards? no read next one

1. also, bear with me .... still learning ..... when you go to change a consumer unit how do you know which board to fit? sensible answers please.

1. on a tt system if you fit dual rcd 30ma c/u you dont need the 100ma rcd

 

[wannabesparky]

1. on a TT system do you still need 100ma on the new 17th edition consumer units

No you dont

1. Do you still need a time delay rcd on a TT system with these new boards? no read next one

1. also, bear with me .... still learning ..... when you go to change a consumer unit how do you know which board to fit? sensible answers please.

1. on a tt system if you fit dual rcd 30ma c/u you dont need the 100ma rcd

what if it is a tncs stystem or tns , how do i know what kind of board to fit?

 

[saveloy]

Re: cu change

Have a look at this guide from Hager. (download pdf). 17th Edition Consumer Unit Guide Hager

Gives a good guide to different CU configurations. I always use a board that leaves a couple of spare ways on it in case additions are needed later. Hope this helps.

 

[piz]

tns tncs or tt can all have a dual rcd board fitted

 

[wannabesparky]

Re: cu change

Have a look at this guide from Hager. (download pdf). 17th Edition Consumer Unit Guide Hager

Gives a good guide to different CU configurations. I always use a board that leaves a couple of spare ways on it in case additions are needed later. Hope this helps.

1. How do you know what main fuse is in the main cut out if it isnt labelled up?
2. How can you tell what size the tails are?

1. How do you know what main fuse is in the main cut out if it isnt labelled up?
2. How can you tell what size the tails are?

 

[benji]

1. If there was no seal you would be able to see
2. You should be able to tell the difference between 10.mm/16mm/25mm

yours benji

 

[Spudnik]

What is the relevance with cut out size when swapping put a CU?????????

 

[electricAl]

Re: cu change

1. How do you know what main fuse is in the main cut out if it isnt labelled up?

We can`t be expected to know the unknown (there again, sometimes we are...)

If you`ve not been given authorisation to remove the seal (see Jason/Saveloy`s posts in a recent thread on this topic) then you couldn`t reliably be sure of it`s capacity. So either estimate & state as such on cert, or simply `unknown`

Difficulty there is, your diversity calcs would be based upon an unknown (but educated guessed at) quantity.

Simple really

 

[saveloy]

Re: cu change

1. How do you know what main fuse is in the main cut out if it isnt labelled up?
2. How can you tell what size the tails are?

1. How do you know what main fuse is in the main cut out if it isnt labelled up?
2. How can you tell what size the tails are?

1. If you are unsure (ie main fuse sealed) then err on the side of caution and make sure your main switch is rated at 100amps. this ensures that it won't be overloaded on a single phase domestic supply.
Personally When changing a board I would pull the fuse as a matter of safety. you would then see what rating the fuse is. As a rough guide 16mm tails (from main fuse ) normally indicate either a 60 or 80 amp fuse and 25mm 100. But never assume always check

2. Experience will tell you what size the tails are. You are only allowed to replace the tails from the meter onwards. The tails between the fuse and the meter are the responsibilty of the DNO and should not be touched. If you are unsure you can always compare with other tails/cable if you have them to give you an idea.

EDIT to add. I work in SSE DNO area and they are ok with registered contractors pulling fuses as long as you inform them. Be careful some DNO won't let you cut seals to pull fuses. On the other hand if there is no seal fitted they wouldn't know. Just inform them when you've finished that the seal is missing

 

[wannabesparky]

What is the relevance with cut out size when swapping put a CU?????????

i was asking because, what if there were a couple of rewireable fused boards that needed taking out and a new 17th edition board put in their place, i am learning so bear with me please.

 

[Spudnik]

ah fair enough.

With a CU swap it is not vital that the rating of the cut out is established, because normally, you would not be adding any additional load.