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LastManOnline

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A customer rearranged some kitchen units, exposing a copper section of the main waterpipe. It's just over a foot long(rest of house is Qualpex). However it's unbondedI carried out an Fli test and it maxed out. I next carried out an IR test and got a, reading of 7000 ohms. A little high for a waterpipe I thought. Double checked with a second test and got same reading. OK, a little bit of copper pipe running in some very dry concrete.
However the reading is still way to high to leave it unbonded and the CU is right at the other end of the house.

What other options might I have?
Get a plumber to replace the copper with Qualpex?
Bond the copper pipe to a local socket?
All suggestion welcome
 

Pretty Mouth

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Bonding it to a socket would mean the bonding conductor (in this case the CPC of the socket circuit) would be undersized.

Could you run the bonding conductor externally? I use a black single for this, for minimum visual impact.

Alternatively, you could leave it unbonded. Some suggest the maximum resistance between MET and metallic part, for it to be considered extraneous is 6667ohms, based on the following calculation:

R=V/I
R=230/0.03
R=7667ohms for the whole fault loop, including human body, for a maximum of 30mA to flow.
Minus an assumed 1000ohms for the human, leaving 6667ohms.
 
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LastManOnline

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Bonding it to a socket would mean the bonding conductor (in this case the CPC of the socket circuit) would be undersized.

Could you run the bonding conductor externally? I use a black single for this, for minimum visual impact.

Alternatively, you could leave it unbonded. Some suggest the maximum resistance between MET and metallic part, for it to be considered extraneous is 6667ohms, based on the following calculation:

R=V/I
R=230/0.03
R=7667ohms for the whole fault loop, including human body, for a maximum of 30mA to flow.
Minus an assumed 1000ohms for the human, leaving 6667ohms.
You have given me some very helpful food for thought there. ?
 

timhoward

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Is there any existing bonding in the same room such as gas or other water pipe?
I once cut bonding short of a clamp, butt crimped a new length on, looped around the original clamp and ran on to where I needed it.
 

timhoward

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Another thought - if we are calling this supplementary bonding we are after a 2.5mm bonding conductor (if covered). Is there a 6mm T+E cooker circuit in the room with a 2.5mm cpc?
 

telectrix

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Bonding it to a socket would mean the bonding conductor (in this case the CPC of the socket circuit) would be undersized.

Could you run the bonding conductor externally? I use a black single for this, for minimum visual impact.

Alternatively, you could leave it unbonded. Some suggest the maximum resistance between MET and metallic part, for it to be considered extraneous is 6667ohms, based on the following calculation:

R=V/I
R=230/0.03
R=7667ohms for the whole fault loop, including human body, for a maximum of 30mA to flow.
Minus an assumed 1000ohms for the human, leaving 6667ohms.
I use 23K as that allows only 10mA.
 

pc1966

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My first though it just box it in as @DPG suggests.

However, if there are other water pipes nearby that are bonded to the CU (so resistance under 0.1 ohm or similar) than bonding it to them would be much the same as if it were continuous pipe.
 
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LastManOnline

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Box it in?

(That's some in-the-box thinking)
Good idea. But there is a, stopcock which needs to remain accessible.
(That's some in-the-box thinking)
I have wrestled with this for 2 weeks vacillating from "it should be fine left unbounded" to mayby not". Mayby not " has won the day for reasons outlined below..

Am unhappy with a 7000 ohm res for the reasons TEL outlined. In fact the new Irish t&e with its increased earth size means the max touch voltage under a line to earth fault will be 115, meaning the effective resistance is 14,000 ohms. But that's still well below 20,000.
Secondly, under a broken neutral scenario, touch voltage could be back up almost mains voltage again. So bonding is the only option I feel.
The only "simultaneousely accessible" metalwork is the dishwasher. I intend to run a bond to its socket. I appreciate that this may not fulfill the letter of the law,but considerer it electrically sound for the following reasons

1)It mitigates electric shock under all fault scenario's

2)A 7000 ohm resistance prevents any heat damaging fault currents from been either exported or imported

3) Because of (2) a main bond adds no extra protection

What say ye?
 

timhoward

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What say ye?
I believe GN8 states the same 23Kohm figure that Tel said above (500v IR test between MET and the item in question). So I agree something needs to happen.

If there's really no practical way to do it properly, including external cable runs, I'd probably prefer sorting it with the plumbing; put a compression coupler onto the copper, then change to john guest plastic pipe, put a new stop cock on the plastic section, and box in the original copper stop cock and pipe. If that all fits in the required space of course.
 

timhoward

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I shouldn't admit this but my brain wandered to trying to think of an inexpensive plumbing accessory that requires an earthed electrical connection that could be installed inline on the pipe and legitimately powered by a spur....thus bringing the potential to earth down so when you test it its suddenly fine...!
I couldn't come up with one, a two port zone valve locked open was the closest I got!
 

telectrix

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I shouldn't admit this but my brain wandered to trying to think of an inexpensive plumbing accessory that requires an earthed electrical connection that could be installed inline on the pipe and legitimately powered by a spur....thus bringing the potential to earth down so when you test it its suddenly fine...!
I couldn't come up with one, a two port zone valve locked open was the closest I got!
self tapper through pipe, ring crimp to stop the leak. (well, wet-pants screw up our gear. REVENGE TIME).
 

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