Tpn

[dave-gardiner]

Steel DB TPN - 16mm TPN singles connected to internal isolator then exit DB through grommeted hole out to a meter then return through a different hole and connect to busbar. Is this ok or should all cables exit and enter through the same hole?

 

[telectrix]

why is the meter not installed upstream of the DB?

 

[R1CH-G]

For metal-clad boards make sure that the singles are NOT leaving through individual holes - you'll end up with eddy currents, unless you slit the holes to join them together and avoid eddy currents. Isn't there a piccy of this in the NIC handbook (I know there used to be!)

 

[dave-gardiner]

the meter is used for monitoring student accomadation on a agricultral site.

 

[dave-gardiner]

3 phase and neutral exit through one hole and all return through another

 

[yellowvanman]

As previously been said all the outgoing singles (3PH + N) should go through the same hole, similar for the incoming singles, although not necessarily the same hole!

 

[dave-gardiner]

is this in writing anywhere? its just the site is being electrically tested and this came up.

 

[telectrix]

just give the students the key to the switch room. they will soon bypass the meter. problem solved

 

[yellowvanman]

Dave

The closest BS7671 comes to that is 521.5.2 but it doesn't say anything about entry holes.

If you've got Darryle Locke's book on the 17th Edition (ECA) then there is mention in there of Eddy currents.

 

[R1CH-G]

Look in the NIC handbook - it was in there for certain (at least it was in the 16th edition version!)

 

[nick611]

if all 3 phases go out through one hole and return together through a different hole it will not cause eddy currents the same as a 3phase swa through its own hole will not