Parallel Feeds

[jamieb100]

Doing an EICR on a building and a sub board has two 4mm twin and earths feeding it. Cables are connected into same breaker in main db but take different routes to get to sub board. Is there anything in the regs regarding as I cant find anything.

Cheers for any information or advice.

 

[Rockingit]

Cables should be the same size and the same length, other than that you're probably OK.

523.7

 

[Engineer54]

As Rockingit stated parallel sub-main feeders need to be of equal size, equal length, and be of the same construction. Ideally they should follow the same route too. There is a very good chance when they don't follow the same route/path, that they won't meet the equal length criteria of parallel supply!!

 

[jamieb100]

Thanks for the information, just one other question, should I put it down as an observation and what what code would I give it?

 

[Engineer54]

Thanks for the information, just one other question, should I put it down as an observation and what what code would I give it?

If you test the resistance of each leg of the parallel supply, you will know for sure if they are of equal length. I wouldn't mind betting that they are not!! It's your call, if your going to code it without testing though!!

 

[jamieb100]

I have tested both cables and r1+r2 for cable 1 is 0.36ohm and r1+r2 for second cable is 0.41ohm

 

[Engineer54]

I have tested both cables and r1+r2 for cable 1 is 0.36ohm and r1+r2 for second cable is 0.41ohm

There you go then ...lol!!

 

[JD6400]

As Rockingit stated parallel sub-main feeders need to be of equal size, equal length, and be of the same construction. Ideally they should follow the same route too. There is a very good chance when they don't follow the same route/path, that they won't meet the equal length criteria of parallel supply!!

I have always thought that you are not allowed to have any joints in them as well , but can not remember where i have either heard or read this !?

What would be your thoughts on this Engineer54 ?

Thanks , Dave

 

[Engineer54]

Joints on a dual 4mm parallel circuit, i wouldn't like to think so!! On substantial parallel supplies, i've seen joints put in direct buried cables, but normally because of damage repairs etc!! Nothing basically wrong with permanent joints in any cable, ...if carried out correctly with an appropriate joint...

 

[JD6400]

Thank for your take on it !

I for the life of me can not think where i heard it so maybe i just imagined it ?

It does sort of make sense in a way , but as you say on a professionally made joint it should make no difference .

 

[Knobhead]

I'm not going back digging up miles of cable because it's got a few joints in it!

 

[Engineer54]

Perhaps your thinking about tap-off joints, on one of the parallel cables, to feed something else?? That's certainly not allowed!! lol!!

 

[JD6400]

I'm not going back digging up miles of cable because it's got a few joints in it!

Unfortunately Tony i did do just that , and it has nearly broke us !:nonod:

 

[JD6400]

Perhaps your thinking about tap-off joints, on one of the parallel cables, to feed something else?? That's certainly not allowed!! lol!!

That may well be what it was !

 

[Knobhead]

Unfortunately Tony i did do just that , and it has nearly broke us !:nonod:

Was that the job you mentioned on here a while back?

 

[jamieb100]

I have traced both cables from start to finish and there are no joints in them and the outer sheath looks in good condition. Still not sure what code to give it

 

[Jay Sparks]

With a difference of 0.05 ohms, the extra length cant be that much. I mean the difference could be down to slight movent of the croc clips when testing. Look in the OSG and do a few calcs and you will see how long each cable is. When you measure end to end on a ring, the L N results can be within 0.05 ohms and still be ok. At worst, going by what you have described, I would say C3 but as others have said its your call. Some wouldnt even code it. I may not code it if I was acctually on site looking at the whole picture.

Jay

 

[capitolltd]

You can work out the load sharing of the conductors, but a simple clamp meter test should suffice. Assess the load and the supplying PD and make an engineering judgement based on your findings.