Piggy Back Off Main Power Feed

• #1

Hi Guys,

Came accross an install today where a new 2 way board has recently been installed to make room for a new shower circuit (Db1 - 16th edition full board).

How the 'electrician' had wired it was by using 16mm tails from DB1 main switch which now has 25mm and 16mm crammed in there (please note there are no cores cut). I no this is not the correct way but now the customer is asking which regulation this does not conform too (basically I don't think he trusts me).

The main service fuse was marked up as a 1361 type ll 60amp.

Can somebody please shine some light on this please, I don't think ill be reattending to split the tails with a henley block anytime soon

Thanks

• #2

I no this is not the correct way but now the customer is asking which regulation this does not conform too

tell the customer that the rules are has follows .
1) get the numbty to come back to put the tails in tail block.
2)over crowding the manufactures instalment of the isolator.
3) putting a strain on the isolator .
4) walk from the job and tell him you will not be back.

Last edited: Feb 15, 2020

• #3

If he doesn't trust you walk away. I wouldn't do work for anyone if I had the slightest doubt about trust, either way.

• #4

I'd tell the customer it's not right and not designed for that and needs sorting or not do the job mate,

• #5

Could try and use 434.3.iv

Then advise that the DNO stipulates the tails installation be changed to meet thier requirements - may only apply to DNO tails but let's not split hairs, customer wants a reg number and you've now got one.

• #6

I'm not sure there is. More likely its what the manufactures instructions would say. I'm thinking of the internal fly leads for feeding RCD's, with the welded cable ends. You can put more than one cable in an mcb. Not that I would try & put two large diameter cables in one terminal.

• #7

It comes down to engineering judgment really doesn't it.....you can run 2 radials or both legs rfc from an mcb but realistically you wouldn't start adding more circuits for practically.....I can't imagine that main switch with a 25 and 16 mm cable in it is clamped down to well?

• #8

I wonder if he did it "live"? Or is the Fuse seal broken? How is it fed into the Board with a proper Tail gland?

• #10

Hmmm

come across this quite a lot but often cores have been chopped off to get both cables in

• #11

If we all 'walked' every time there was a non compliance on an existing installation which a client was reluctant to spend money on nothing would get done.
Ridiculous post

the op has pointed out to a customer that the 25+16=41 mm tails are put in a
isolator ,and there for the design are made for 25mm tails not 41 , you could get away with it many years ago, but not like the olds wylex isolators with a couple of screw to terminate the tails .

• #12

most main switches are rated for 35mm cable and 25 plus 16 is a bit too big, depends on which con unit it is.

• #14

While I accept this sort of thing is not uncommon and even allowed in regs subject to having a fault protection capable of protecting the cable to the sub-main, the question would arise what is the main fuse? For 16mm tails let's hope it's not 100A! But then I imagine taking in to account manufacturers installation instructions most of us would baulk at doing this as we would not comply with said instructions, wouldn't we? I personally don't like putting different size cables in the same termination due to difficulties in securing a good termination.

• #15

@digital_boy You could refer to regulation 462.1.201 "A main linked switch or linked circuit-breaker shall be provided as near as practicable to the origin of every installation as a means of switching the supply on load and as a means of isolation."

• #17

I didn't say it was compliant, but if the OP is carrying out other work and the customer does not want him to remedy this, he just needs to verify that the connection shows no sign of thermal damage, and is secure and tight.....and note exactly that on his cert.
Walking away because of a relatively minor deviation from the regulations which does not form part of the work being carried out is plain daft.

If it leads to argument/disagreement/lack of trust you're better off walking away. You ridicule someone...for stating their view, without taking this into account. All situations are different but, in this one, it seems the OP is worried that there is a lack of trust.

• #19

I would go with manufacturers instructions should be taken in to account. Can't remember the reg number.
Then find a pdf of the relevant MI.
Although it's R.A.F. It's something I've seen a few times with no ill effects.

• #20

Can't remember the reg number.
Then find a pdf of the relevant MI.
Although it's R.A.F. It's something I've seen a few times with no ill effects.

Could try and use 434.3.iv

Then advise that the DNO stipulates the tails installation be changed to meet thier requirements - may only apply to DNO tails but let's not split hairs, customer wants a reg number and you've now got one. View attachment 55793

Give the DNO a call, advise them what you can see and ask if they permit consumer tails to installed that way, if they don't then there's your deviation/breach of reg 434.3.iv.....no?

• #21

Overload protection can be omitted and fault protection will be adequate

I am not sure I agree we can dismiss the idea that the tails need overcurrent (as opposed to overload) protection. In terms of the fixed load ahead yes indeed but the tails at 16mm would not meet regs in the thermal destruction aspect in the case of a short. In others words what would melt first the fuse or the tails?

• #23

It isn't feeding a fixed load, it is a two way consumer unit.

• #25

The OP said it's feeding a shower, so at the time of the installation it is a fixed load. If someone else adds another circuit it is their responsibility to verify compliance for whatever they are adding.

He said it is a two way board which supplies the shower. The supply to this board cannot be considered a fixed load.

• #27

The shower is a fixed load but the supply to the two way board is not. I agree the 16mm conductors will be fine. Lashing them off the existing board is another matter.

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Source: https://www.electriciansforums.net/threads/piggy-backing-tails.183466/

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