bathroom supplementary bonding.

[andypandy]

A spark told me the other day that when he bonds out a bathroom, he takes all the supplementary bonding wires from extraneous/exposed parts to a earth connnector block local to the bathroom and then runs a 10mm earth cable from this to the earth bar in the installation consumer unit.
I have always believed that when all the equipment in the bathroom was bonded together that the earth wires to the equipment in the bathroom that are inside the ft+e cable were sufficient (as they ensure 0.5 disconnection time) and there was no ned to run an extra earth back to the board.
I cannot seem to find anything in guidance note 7 about an extra earth,however, I have found it mentioned in websites such as this (as shown below)

All non-electrical metal components such as pipes, baths and basins should be joined with supplentary bonding earthing cable that then runs to the consumer unit where it is connected to the earthing block.

Why would sites include this if it was not needed.

 

[Big_Spark]

There is no requirement to connect supplementary bonding in a bath/shower room to the main earth terminal of an installtion. The requirement is that all extraneous conductive metal work be connected to earth via the circuits in the bathroom, ie, light, shaver point, heater etc.

What he may be doing is making life a little easier by simply connecting all the bonding to a common point and then returning that to the main earth terminal so that he does not have to run 6mm bonding cables from each and every electrical accessary in a bath/shower room to the pipework.

using 10mm as the connection is a bit OTT, 6mm would suffice, but at least it has a damn good bonding connection.

 

[ban-all-sheds]

According to the discussion here , according to the IEE, it's not simply that there is no requirement to take the bonding back to the main earth point, it's that you must not....

 

[Big_Spark]

According to the discussion here , according to the IEE, it's not simply that there is no requirement to take the bonding back to the main earth point, it's that you must not....

The IEE does not say you must NOT run a bond back, it states that a bond IS NOT run back to the main Earth terminal.

I would find it very strange if the IEE ststed you MUST NOT do this as there is no reason for this.

If you are unable to confirm that metal pipework is continuous throughout the installation, running a small bonding conductor back to the main bond position would be sensible, HOWEVER if you have done the installion as per the regs and connected the extraneous conductive parts to the earth terminals of the light, and spurs etc within the bath/shower room, then is no requirement to run a bond back.

I know the IEE had a bee in their bonnet the other year about parallel earth paths, and the above could be deemed as introducing one, but so long as the overall resistance will still allow any protective device to operate in the time required than I personally do not see the problem.

 

[andypandy]

I thought 4mm was adequate for supplementary bonding if there was no mechanical protection in bathroom?

p.s. thanks for the prompt replies.

 

[Big_Spark]

I thought 4mm was adequate for supplementary bonding if there was no mechanical protection in bathroom?

p.s. thanks for the prompt replies.

The regs are 4mmsq WITH mechanical protection, 6mmsq WITHOUT protection.

Personally I always do bonding in 6mm regardless, the problem is that the cable may be protected along 95% of its route, but the last part may be exposed and then it should be 6mmsq, so it is easier to run 6mmsq and be done with it.

 

[dingbat]

I thought 4mm was adequate for supplementary bonding if there was no mechanical protection in bathroom?

p.s. thanks for the prompt replies.

The regs are 4mmsq WITH mechanical protection, 6mmsq WITHOUT protection.

"547-03-03 - A supplementary bonding conductor connecting two extraneous-conductive-parts shall have a cross sectional area not less than 2.5 sq mm if sheathed or orherwise provided with mechanical protection or 4 sq mm if mechanical protection is not provided..."

6 sq mm does not come into it unless you are complying with 547-03-01 and 02, which deals with the situation where one or both of the extraneous-conductive-parts is an exposed-conductive-part. The requirement here is that the supplementary bonding conductor must be not less than half that of the protective conductor connected to the exposed conductive part/s. Both of these regs also state, "If mechanical protection is not provided, its cross-sectional area shall be not less than 4 sq mm."

And 547-03 is the regulation referred to in 601-01-01, dealing with supplementary bonding in bathrooms.

I hoep that helps!

 

[Big_Spark]

Dingbat, I take your point, however would you not agree that by connecting, electrically, an extraneous conductive part directly to the earth terminal of a circuit conductive part (as in the box behind a spur or switch), you are making that extraneous part into an exposed part?

I have posed this question to NICEIC Inspectors and members of the IEE at meetings, all have scratched their heads, thought about and then said something similar to, "Well you have a valid point, and it certainly is an interesting one"

However I do take the point that the Regs do state 4mm2 in the situation described.

One of the perils of being old school I suppose, was always 6mm2 when I was younger, and to be honest 99% of sparks I know will tell you the same for the same reasons...even those I employ use 6mm as a matter of course.

 

[andypandy]

6 sq mm does not come into it unless you are complying with 547-03-01 and 02, which deals with the situation where one or both of the extraneous-conductive-parts is an exposed-conductive-part. The requirement here is that the supplementary bonding conductor must be not less than half that of the protective conductor connected to the exposed conductive part/s. Both of these regs also state, "If mechanical protection is not provided, its cross-sectional area shall be not less than 4 sq mm.

How does 6mm come about when the protective conductor to the exposed conductive parts would be say 1.0mm in the case of a light fitting? Or am I severely off the beaten track?[/quote]