Electrical certificate.

[SarahB]

Hi everyone, can I ask a quick question please? If you use a Henley block, and install a separate DB, can you forget about the 100 amp incomer on the original consumer unit? i.e. it wouldn't apply as far as your paperwork is concerned as you've installed say a separate 3 way board? So the paperwork just reflects this part of the installation?
Sorry if this is a stupid question.

 

[telectrix]

yes, your EIC covers only what you install. if you see anything amiss on the existing installation, though, you can put it in the comments box.

edit: and welcome to the asylum. :19:

 

[SarahB]

Thank you ever so much, and I'm sure I'll enjoy it here with all of you helpful chaps
So, if I add a separate DB, and just put a 16 amp MCB on there, then the paperwork will be fine if I say that DB has 16 amps (or of course 16 * 0.4)?

 

[SirKit Breaker]

Hi everyone, can I ask a quick question please? If you use a Henley block, and install a separate DB, can you forget about the 100 amp incomer on the original consumer unit? i.e. it wouldn't apply as far as your paperwork is concerned as you've installed say a separate 3 way board? So the paperwork just reflects this part of the installation?
Sorry if this is a stupid question.

Sarah,

I wont add to the replies as the people who have replied are very knowledgable.
But please never ever assume that your question is "STUPID".

This riles me a lot. There are NO STUPID QUESTIONS. There are only questions which you do not know the answer to, and as a result you ask. You ask you find out, you find out you learn. Please answer this. what is stupid about asking, finding out and learning?

rant over,

Cheers.............Howard

 

[GaryM]

Thank you ever so much, and I'm sure I'll enjoy it here with all of you helpful chaps
So, if I add a separate DB, and just put a 16 amp MCB on there, then the paperwork will be fine if I say that DB has 16 amps (or of course 16 * 0.4)?

Yes, your EIC will relate to the board (eg CU-2) and final circuit(s) you've installed.
Main switch will be the one in your new board and the 16A final circuit will be the only entry on in the schedule of test results.

I'm not getting the 16 * 0.4 part though.

 

[telectrix]

trhink she is referring to diversity for max. load. with the x0.4. sarah, i would put the figure for max load according to the design current of your new circuit, and don't just fit a MCB. you need a double pole main switch as well. and if used for socket outlets, a30mA RCD is essential

 

[SarahB]

Yes, your EIC will relate to the board (eg CU-2) and final circuit(s) you've installed.
Main switch will be the one in your new board and the 16A final circuit will be the only entry on in the schedule of test results.

I'm not getting the 16 * 0.4 part though.

Sorry, the 0.4 part refers to the Electrical Installation Design Guide 'Demand factor g..' estimation method (for diversity). So 16 amps would be multiplied by 0.4 to give a figure of 6.4 amps. So, the question would be, can I install the second DB and fill the paperwork in to reflect that this has 6.4 amps? Thank you all so much.

 

[GaryM]

The schedule of test results will state the circuit is protected by a 16A MCB, not your diversity figure.
You will consider the new circuit for the maximum demand figure on the EIC though.

 

[telectrix]

but don't use 16 x 0.4 as your demand figure. use your calculated load, based on what you have designed the circuit load to be.

 

[SarahB]

Thank you both. So I WOULD use 16 amps on the certificate then? Sorry, stupid thing to say. I realise that the schedule of test results would state a B type MCB, and a 16 amp circuit. It's the demand figure I'm referring to.

 

[GaryM]

If you're thinking of maximum demand and using the sum of all MCB's for the figure (just one 16 on your new CU though) then no, don't do that.
Also the MD will be for the whole installation, including the main consumer unit.

 

[telectrix]

forget the 0.4. you use that on a multiple circuit CU where you take 100% of the largest load and add 40% of the rest added up. your max. demand is 16A as that is 100% of the largest ( and only ) circuit.

 

[SarahB]

Also the MD will be for the whole installation, including the main consumer unit.

Right, this is the bit I thought I had got to grips with. I thought if I used a Henley block, and added a separate DB then the main consumer unit becomes irrelevant as the new supply isn't going through that. Or is it? My concern is if that original consumer unit has a 100 amp main fuse, and it's almost at capacity, my adding an extra DB might tip it over the edge. My understanding was that this new DB would be fine. Sorry, this use of Henley blocks is quite new to me.

 

[GaryM]

It's the maximum demand for the whole installation you need to consider when making additions to an installation.
Imagine your property is supplied with a 80A main fuse and you have two consumer units, each with a maximum demand of 50A. That wouldn't go well with the rating of the main fuse.

 

[SarahB]

It's the maximum demand for the whole installation you need to consider when making additions to an installation.
Imagine your property is supplied with a 80A main fuse and you have two consumer units, each with a maximum demand of 50A. That wouldn't go well with the rating of the main fuse.

Thank you Gary, that makes sense. I was thinking of the main incomer on the original consumer unit rather than the main fuse. If the scenario you mentioned was to occur, would it be fairly simple to upgrade the main fuse?