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Phase Converter/Bridgeport Wiring Help

I've just taken delivery of a Transwave phase converter and need some advice befoe attempting to connect it to the Bridgy.

Coming out of the machine control cabinet is an SWA cable with the

3-off phase wires in it, but no others. The brass gland into the cabinet is making good contact with the armouring wire, and the gland at the other end where it was obviously disconnected from the isolator box is the same.

Would I be correct in assuming that this connection between the armouring & gland and the between gland/control cabinet and gland/isolator box was used to provide an earth for the machine?

As such, (and I'm assuming the Bridgy needs an earth..) would I also be correct in assuming that I cannot use this cable and need one with a facility to take an earth from the transwave supplied 5 pin plug (3 phases, earth and neutral) to an earthing point on the machine cabinet?

I have already identified L1, L2, & L3 in the control cabinet to connect the converter in accordance with the instructions, but as you know my electrical skills are pretty non-existent and I don't want to do something silly...

Thanks for your help

Peter

Reply to
Peter Neill
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gland

isolator

The Bridgeport only needs the 3 phases and earth - the neutral isn't used in the standard wiring. Normal SWA cable relies on the armour for earthing (though personally I prefer a bit of copper so use 4 core not

3!). Using the armour is fine for an 'indoor earth', it's just that I get a bit twitchy if it is exposed to weather.

It is probably easiest to get a metal conduit box with a suitable hole for your SWA gland (probably 20mm but may be 25mm) screw it to the wall, and terminate the SWA in it, running a 3 phase and earth cable as a flying lead with a plug on the end to the Transwave. If you want to get really posh the metal conduit box could be replaced with a three phase isolator switch in a metal enclosure, though you can isolate easy enough at the Transwave.

AWEM

Reply to
Andrew Mawson

Oh, and a follow up ! You need to ensure that the 'generated phase' from the Transwave isn't used to power the contactors in the Bridgeport. This phase doesn't have significant volts on it until a motor is spinning, so you get a chicken and egg effect - no volts, no contactor pull in so no motor so no volts ! The coils of the contactors are probably across L1 and L3 - that is the way the Bridgeport diagram shows it..

(This assumes a static convertor - if it is a rotary then ignore the above)

AWEM

Reply to
Andrew Mawson

Actually SWA does not 'rely' on the armour, it may or may not use the armour to carry the earth (technically not called the earth but the Circuit Protective Conductor or CPC), it's perfectly normal to use a core for the CPC but in this case the armour must also be connected to the CPC at one end in case the cable is damaged. Which way you do it does have an affect on Zs (the earth fault loop impedance) and this can affect your choice of protective device, particularly important if you need to use a type C or D MCB to cope with motor surges, though a short run from the wall to the machine like this won't make a difference.

Quite right, except that the box does not have to be metal, the SWA gland should come with a tag that you can bolt a crimp terminal to, thus connecting to the armour regardless of the case material. Isolator boxes are now most commonly plastic so these have to be used if only to ensure the armour is connected to the CPC, it's quite common to see SWA coming into and going out of an isolator on adjacent holes so the tags can be bolted directly together.

Greg

Reply to
Greg

I've made that mistake - you only make it once!

Charles

Reply to
Charles Ping

message

affect on Zs

In my experience SWA glands into plastic boxes are a disaster - the walls of the boxes are far too flimsy. Even tightening them up can be a fraught time!

AWEM

Reply to
Andrew Mawson

Plastic enclosures are the norm now, isolators, emergency stop buttons etc all come in plastic cases, even large 3 phase distribution boards do. The obvious reasons are that they don't rust, punching out holes is easier, don't need to be bonded to a CPC and hence don't have to be tested for continuity.

Greg

Reply to
Greg

Gentlemen,

Thank you very much for the advice. If I can summarise to make sure I've understood correctly:

Option 1 - use the existing SWA cable and glands into a metal box with the armouring as the Earth/CPC carrier.

Option 2 - get some new 4-core (HOFR or Sy-Flex?) and connect the Earth/CPC directly.

I also have an MEM 32A Isolator switch box with a fitted 5-pin socket coming off the bottom (another item scrounged from the factory shutdown). Would I be OK to use this providing I de-rate the internal fuse links down to 16A to match the supplied plug? This way I can then have a plug in 3-phase source for any other motors I may use.

On the subject of connecting the right phases for the converter (it is a static unit) I checked the lines into the contactor and got continuity across L1 & L3 so guessed this must be feeding the control coil. Bearing in mind my normal dyslexia when it comes to electrics/electronics I felt quite pleased with myself:)

Peter

Reply to
Peter Neill

message

socket

internal

control

Yes, sounds eminently reasonable

AWEM

Reply to
Andrew Mawson

That all sounds fine, just one point and I may have misunderstood you, but the 32A and 16A 5 pin connectors are not compatible so if the 32A isolator is fitted with a 32A socket as you would expect then you can't fit a 16A plug into it. I would stick to 16A sockets throughout as these will handle more than enough for a domestic workshop. Oh and don't forget that the cable as well as the plug have to be rated at least as high as the fuses.

Greg

Reply to
Greg

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