Ask The Trades - Print Page

Ask The Trades
https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> Aother cross bonding question! https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1314106997 Message started by trowelhead on Aug 23^rd, 2011, 2:43pm

Title: Aother cross bonding question!
Post by trowelhead on Aug 23^rd, 2011, 2:43pm

Hi all,
i am asking this question for a mate who is working on a BT contract,fitting there new fibre cabinets at the roadside.

At present they dig up the path etc and concrete in these new metal cabinets where BT tell them too.These cabinets are then linked (by BT) via there telephone cables to the smaller existing cabinets.(the ones you see BT engineers fiddling about in and looks like spaghetti!).The new cabinets he installs have 230v and the existing cabinet has only the telephone voltage.
BT says that if the new cabinet is less than 5 metres from the existing cabinet it requires cross bonding.Fair enough.

Retrospectively BT, are now asking my mate (for no payment) to go back and bond any site he has worked on if there is a disused,empty BT cabinet inbetween the fibre cabinet he has installed and the existing working telephone cabinet.
The new cabinet and existing telephone cabinet might be 6 metres apart but,the defunct cabinet might be in the middle of both making a gap of 3 metres either side to each cabinet and therefore they want all 3 bonded together.

These unused cabinets are completely empty and are just metal shells concreted into the roadside,nothing is or will be run from them.
Why does it have to be bonded to the other 2 cabinets,after all if there was a lampost or any other metal object in its place you would not need to bond to that? (i know they couldn't because it is not theirs!!)

If you do understand what i have asked and,you can quote me a reg' that will stop him having to do this we would be more than grateful.

I hope it makes sense :-?

TH

Title: Re: Aother cross bonding question!
Post by Lectrician on Aug 23^rd, 2011, 4:54pm

There is no BS7671 reg that could come into play here at all - BT likely have their own specifications, based on some form of legislation, and these would need to be met.

I am not sure what legislation governs this type of highway works...

Title: Re: Aother cross bonding question!
Post by trowelhead on Aug 23^rd, 2011, 5:13pm

Thanks Lec.
Is it a good or bad thing though,to intoduce something into the bonding arrangement that has no direct link to the items being bonded,after all you would n't bond your bathroom pipes to your metal bedroom windows?

My mate hates BT!!!

Title: Re: Aother cross bonding question!
Post by wozzy on Aug 23^rd, 2011, 6:08pm

I hate BT.

This maybe for some reason other than additional shock protection :-? EMC, interference? no idea.

As far a shock goes the person will most likely be standing on general mass of earth putting another potential on it wont be great for the same reason we try not to export the earth.

Title: Re: Aother cross bonding question!
Post by CWatters on Aug 23^rd, 2011, 6:49pm

Google suggested the first part of this thread might be relevant..

http://www.diynot.com/forums/viewtopic.php?t=285631&sid=ade517950fc2d66275cf4e5e9b06cb57

elsewhere there are references to the supply to housings being covered in PO4/1 (1988 vintage?). Perhaps that also covers earthing.

Title: Re: Aother cross bonding question!
Post by Goodsparks on Aug 24^th, 2011, 7:17pm

Quote:

I would say good in this situation, given that the cabinets will be linked electrically, the voltages present in both will probably be above ELV and the cable sheaths / internal functional earth conductor in the bt cables won't necessarily be at local earth potential. I certainly don't think it would cause any harm....

Title: Re: Aother cross bonding question!
Post by trowelhead on Aug 24^th, 2011, 9:05pm

wrote on Aug 24^th, 2011, 7:17pm:

Quote:

Thanks but,you have mis understood.The 'middle unused' cabinet is empty.It has nothing but spiders in it!
The 'working' cabinet is 5 metres away and therefore 'out of range' from the new fibre cab.

Title: Re: Aother cross bonding question!
Post by L.Spark on Aug 25^th, 2011, 12:10am

It may be empty now but they may decide they want to use it at a later date, e.g. they might be keeping their options open.

Ultimately though, big companies can set their own requirements (specifications) within reason, and these would have to be followed as part and parcel of working for them.

What you should actually be asking/finding out is DID they (BT) specify that this cross bonding needed to be done at the time the quote (if there was one) was approved. If they didn't, then obviously he's entitled to now charge them for this works. But if they specified it and he quoted for it then he's going to have to do it.

Title: Re: Aother cross bonding question!
Post by wozzy on Aug 26^th, 2011, 6:41pm

I dont understand this unless someone can reach three metres to touch each cabinet or there is a bonded grid they are standing on it wont achieve much?

Title: Re: Aother cross bonding question!
Post by CWatters on Aug 29^th, 2011, 5:26pm

Customer allways right unless they want you to go back and do it free (as in this case). I think I'd want to look at the contract.

Title: Re: Aother cross bonding question!
Post by Flashbang on Aug 30^th, 2011, 3:44pm

CWatters wrote on Aug 29^th, 2011, 5:26pm:

Customer allways right unless they want you to go back and do it free (as in this case). I think I'd want to look at the contract.

Hi
I agree with CW, your friend needs to carefully read the contract.
If it states he or any sub contractor he employs are responsible for providing all forms of earthing (incl. cross bonding) then that's it. If not then the work requested is a variation to the contract and he is entitled to seek all costs involved in carrying out this variation. Or BT can let a new contract to undertake the work as a totally separate item!
But the first thing is check word for word the actual contract signed and in force.