On Monday, 1 May 2017 17:01:01 UTC+1, ARW wrote:
On 30/04/2017 18:56, Tim Watts wrote:
On 30/04/17 18:03, ARW wrote:
On 30/04/2017 16:33, Tim Watts wrote:

What's your opinion on that (long SB wire routing)?

It's possible to work out a maximum touch voltage between two metallic
objects (one at 230V and one at 0V) bonded by a 4 mm earth cable.

However I have been in the pub for 6 hours (mt apologies to Wakefield)
and I'll pass on trying that calculation today.

Thanks Adam.

If that's all it comes down to, fair enough.

However, the potential difference would also depend on what's connecting
the Ov and 230V sides. 4mm2 is not much compared to the area of copper
in a 15mm water pipe which is about 32mm2 for 0.7mm walled pipe.

OTOH 4mm2 is vastly larger than the 1 - 1.5mm2 CPC in the lighting
circuit which also has a long run to origin.


Less true with a shower though that might have a 4mm2 CPC and larger
live conductors.


So how is the theory of supplementary bonding handled? Presumably some
allowance must be made for ADS being operational?

You keep the touch voltages between two objects to less than 50V.

If the ADS is still working in 10 years time (ie the RCDs) then fine.


The maximum potential difference with EEBADs is down to the resistance
of the 4mm cable between the two points connected by that cable.

And yes I would expect an MCB or fuse to trip before this sort of thing
happened.

No matter what you design for some pillock will still manage to mess it up.

PSCC of domstic wiring is anything upto 6kA.
4mm2 voltage drop is 5.5mV/A/m or 5.5v/kA/m
You can calculate from that, adding in the R of the supplying lighting circuit.


NT