Mains voltage and ebus

[Andygasman2010]

Alright lads, I'm over from the gas forum for a bit of help.

I'm looking to fit a boiler which has mains and ebus and I'm wondering if it's allowable under part P to use the same cable with 240vac AND ebus in it.

I know seperate cables are the best way to go but I'd like to try it mixed so I can use an existing cable making the installation much easier.

Cheers!

 

[Taylortwocities]

They have to be separate. That is a requirement of BS7671.
eBus is 24v DC.

In fact the Worcester guide to eBus specifically states:

"To avoid inductive influences, lay all cables
carrying low voltage lines of 230 V or 400 V
separately (minimum spacing 100 mm)."

 

[Andygasman2010]

Thanks! All the best to you too.

 

[AdrianUK]

They have to be separate. That is a requirement of BS7671.

I don't think that is correct. There is no regulation which prevents different voltages existing within the same multi-core cable - the only requirement is that ALL cores must be insulated for the max voltage present on any conductor.

The manufacturers instructions may well state that separate cables are needed (prob for electrical noise reasons) but thats something totally different.

 

[Alarm]

Put it another way, segregation.

 

[Taylortwocities]

eBus is effectively Band I

Your 230V supply is Band II

Andygas wants to use the same cable for eBus and 230v

Now, go and read 528.1 and you will see that the only case where Band I and Band II can be in the same Multicore Cable is if the Band I circuit is enclosed in an earthed metal screen.

So the answer is

TTC

 

[AdrianUK]

528-01-01 Neither a Band I nor a Band II circuit shall be contained within the same wiring system as a circuit of nominal voltage exceeded that of low voltage unless every cable is insulated for the highest voltage present or one of the following methods is adopted :

i). Each conductor in a multicore cable is insulated for the highest voltage present in the cable or is enclosed within a metalic screen.......

 

[Alarm]

Even with that shielding I would still not trust data being send. Seen enough items go pop from induction and spikes.

 

[AdrianUK]

Even with that shielding I would still not trust data being send. Seen enough items go pop from induction and spikes.

No argument, I agree that for functional reasons it is wise but is ISNT against the regs!

 

[Alarm]

Fair enough, I never agreed whether it was or not. Just the way I have been trained and experienced.

Cheers

 

[Taylortwocities]

Me too, but I will repeat the instructions from the manufacturer

"To avoid inductive influences, lay all cables
carrying low voltage lines of 230 V or 400 V
separately (minimum spacing 100 mm)."

 

[AdrianUK]

I agree. And they should be followed. I suspect that they have done this for noise/interference reasons.

My beef was that you stated that it was against the regs...... it isnt. Good practise - Yes, Wise - Yes, Good workmanship - Yes. Against the regs NO.

Too many sparks, when doing PIRs or looking at an existing install simply say "can't do that - its against the regs" without being able to back-it up with a regulation.

 

[Andygasman2010]

Yea it's the regs that I was getting at. I know it'd be much better to have a seperate cable but I wasn't sure if it was a regs issue or just best practice.

Thanks

 

[AdrianUK]

OK, but to be fair to my right hon. friend Taylortwocities .... it is also a requirement of the regs that the manufacturers' instructions are followed .....

 

[ban-all-sheds]

And that's a two-fold requirement.

First there's the regulation which says that MIs should be followed.

And second there's the one about good workmanship, and if the maker of a control system tells you to separate the control cables from LV ones by a minimum distance and you don't then you've contravened that one too.