On 09/09/2017 18:11, wrote:

So... Last 2 questions. 1. The bath has the metal framing
connected to one of the motors via an earth lead. However
the earth from the mains connection doesn't seem to be
connected to it. I would have expected to see an earth coming
out of the junction box to connect to the frame. Any
thoughts?

I am not totally clear on exactly what setup you have here, so
I will answer the more general questions...

If the motor units are double insulated (has the double square
logo[1]) then they do not need an earth connection. However
you would normally wire the connection point such that one is
available in case the motor were changed later and the new one
needed one. If needs be, the earth connection can be made of in
a spare non connected terminal block.

[1]
http://wiki.diyfaq.org.uk/index.php/...l_Glossary#1-9

If the motors do require an earth, then the earth of the
circuit feeding them should be included into the supplementary
bonding in the bathroom.

The metal frame of the bath itself is typically not connected
to anything outside of the room itself, and hence not capable
of introducing any potential into the room. As a result it does
not need including in the EQ bonding.

See http://wiki.diyfaq.org.uk/index.php/...ng_and_Bonding

2. I plan to cut into the upstairs ring main to feed this
bathroom. Not a spur buy essentially extending the ring. Any
issues with this?

No that's fine. Note the comments above about including its
earth in the bonding for the room.

Connecting the bath frame to the motor frame does make it able
to introduce 240v in case of fault. I would earth it & feed it
from an RCD or include it in equipotential bonding.

If the motor is class I, then its supply earth should be included
in the bonding, and the motor casing itself does not need
independent connection.

If its class II, then its case is not an extraneous conductive
path,

Whether the motor can conduct to the bath or water depends on
construction details.

Indeed.

Class 2 certainly does not preclude it. Class 2
construction is no more a panacea than the other approaches

Erm, no.

and so bonding the bath would actually increase the risk rather
than lower it.

bonding it to what? bathroom-wide equipotential bonding or the motor
case?

If the motor were class I, then they would be functionally equivalent.
If the motor is class II, then bonding the bath simply means its now an
extraneous conductive path where previously it was not.


--
Cheers,

John.

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