Here is a British 3-phase panel, on a 240/415V 4-wire wye service that is the U.K. standard. The load has since been removed, but do you see a problem with how it was wired?




The full story can be found in the Non-U.S. area here.

Paul, very intesting to see a UK style disconnect. Does the UK also use the US practice of the line=top terminals and load=bottom terminals? Is that the problem here?

No, the line is going to the correct place (follow the above link for an explanation of the switch action).

The problem does lie with the way the feed has been brought to this unit, however. Look toward the bottom, and keep in mind that this is a steel enclosure.

So the “MEM” switch enclosure of ferrous metal would cause an inductive-heating problem where the conductors pass through individual holes in the bottom of the can. 99NEC300-20 warns of this left of the pond.




[This message has been edited by Bjarney (edited 05-30-2003).]

Paul,

That was quite a hint!


Bill

I had spotted the individual conductor entries but just assumed that British power acted differently.

Bob

Hey Paul,
If that's a Star circuit, where's the Neutral?.

No neutral was needed here. The key-cutting machine which ran on this supply just had a 415V delta-connected motor, small enough to have direct-on-line starting rather than star-delta start-up.

Well, it drives on the left-hand side of the conductors and has an accent!


[This message has been edited by pauluk (edited 05-31-2003).]

OK, so the power drives on the left & has a British accent. But you still get eddy currents when each phase is passed thru separate KO's. This is bad practice whichever side of the Atlantic it is done!
Also the open KO on top of the box should be fitted with a blanking grommet.

Paul,
The centre and right-hand wires look like they are going through a rubber grommet.
But the left-hand one looks like it has been fed through a hole that has missed the grommet, you can sort of see a small piece of metal sticking up in front of the wire.
Also, isn't the door on these units, supposed to have a seperate bonding wire on it from the body earthing terminal, to a terminal on the door?.

I wouldn't have thought they would be allowed to have individual wires loose like that not inside an enclosure or conduict. Especially at those voltages.

It looks like the conductor on the left is entering the box without a bushing.
I find it interesting that the ground wire is simply bolted to the enclosure, and not connected to a lug/ terminal strip on the inside of the box.
How much induction heating can take place over a few millimeters of metal thickness at 50 hertz? Though, NEC does say that all phases will be within the same raceway.

The conductor on the left does actually enter through a rubber grommet, although it isn't too clear in the picture. That's not a piece of metal sticking up in front of it -- It's just a loose piece of plaster which had found its way into the box, most likely through the opening on the top which, as David pointed out, should have had a blanking grommet fitted.

Here's a closer view of the bottom section, taken from the thread in the non-U.S. area:

Sorry that it got a little "fuzzed" in the blow-up, but you can just about see that there is a grommet on that left hand entry.

Still a pity that someone brought in one phase per knock-out, though.

Interesting point about a grounding strap on the door. I've never seen an MEM unit of this type with such provision, although when the front is closed the screw on the left probably tightens it down securely enough to give a good ground.

The cables run in an open fashion like this between meter and panel is the way you will usually see it done on residential and small commercial sercvices like this one. The phase (and neutral) conductors are double insulated.

[This message has been edited by pauluk (edited 06-06-2003).]

Paul,
There's no marking of Phase sequence on the incoming wires, is this allowed in the UK?.
You wouldn't get away with it over here.