Pilot pin on 63A BS4343 connectors

[SimonH2]

Does anyone here know how the pilot pin on 63A (and larger ?) BS4343 connectors is supposed to be used/wired ?

It's more from curiosity than any specific need - I dislike having things where I don't know what they're for ! While we have a 63A inlet for an alternative supply to our server room UPS, the only use we've made for it (and are likely to in the foreseeable future) is to run the system from the DB in the next unit (we have several offices opened up to one space) when working on the normal supply. We've had to do this in the past when the switch-fuse downstairs in the meter room got "rather hot", and I believe we've a meter change due that we've been putting off. So at the moment, the pilot pin isn't connected to anything on either the cable or the switch on the wall.

All I can find are comments such as "the pilot may be used for a variety of purposes including connection to control circuitry for electrical interlocking" (from the MK Commando datasheet). Others mention the pin, mention that it makes last/breaks first but give no more information than the MK sheet.
From that, I assume there's no standard use for it - so I can just carry on ignoring it. And I assume that in the fairly unlikely case of us hiring a genny, we'd not find ourselves with the genny refusing to power up it's outlet because it's not connected.

 

[Robin0577]

As I understand it, it's intended to be used to switch a contactor such that power cannot be applied until the connector is fully inserted (and is disconnected before the connector can be fully withdrawn). I've never actually seen an installation with that function implemented though, mechanically interlocked switching seems to be far more common practice.

Use of the pilot pin interlock system is apparently more common on the continent than in the UK

However, most of my experience is in the entertainment business so the 63A+ connectors I see are usually on trailing leads or portable distribution boxes, practices may well be different in other industries.

 

[DaftPunk]

I understood too that's it's for some sort of mechanical interlocking or possibly for use as an earthing monitor, but I've yet to see one actually in use.

 

[Lectrician]

Yes, I was led to believe it was used with a 24v ac contactor, using the earth as a return to hold the contactor on. Loose your earth, loose your power.

 

[bernardgreen]

There are several ways the pilot pin can be used. The commonest ( In my experience ) is linking the pilot pin to neutral in the equipment at the far end of the cable. The pilot in the socket supplies a contactor coil, other end of the coil to a phase. The phase(s) supplied to the socket are switched by the contactor. So until the connections are made all the way the equipment there is only neutral and earth on the socket. I have seen the pilot circuit with a switch in the equipment so the cable is not energised until the operator switches on the pilot circuit.

An novel use was coding which plugs could be used in which sockets. The equipment had a resistor between neutral and pilot. behind the socket was a resistor between phase and pilot. These formed a voltage divider. If the voltage on the pilot in the socket was in the right range then the contactor was operated.. If the voltage was not in that range then the contactor was not operated and a "wrong plug" alarm was raised.

 

[SimonH2]

So the consensus seems to be that, as I thought, there's no standard way for it to be used - and I can probably just forget about it.

 

[JohnW2]

There are several ways the pilot pin can be used. The commonest ( In my experience ) is linking the pilot pin to neutral in the equipment at the far end of the cable. The pilot in the socket supplies a contactor coil, other end of the coil to a phase. The phase(s) supplied to the socket are switched by the contactor. So until the connections are made all the way the equipment there is only neutral and earth on the socket.

...except that, presumably, if done as you describe, the pilot at the socket would be at phase potential (via the contactor coil) until the circuit was completed wouldn't it?

Kind Regards, John

 

[bernardgreen]

the pilot at the socket would be at phase potential (via the contactor coil) until the circuit was completed wouldn't it?

Yes , or it can be a 24 volt control circuit supply but that adds the complication of mixing ELV and LV circuits in the same plug.

 

[JohnW2]

the pilot at the socket would be at phase potential (via the contactor coil) until the circuit was completed wouldn't it?

Yes , or it can be a 24 volt control circuit supply but that adds the complication of mixing ELV and LV circuits in the same plug.

Not only mixing ELV and LV in one plug but, presumably, the arrangement you described would requite the ELV and LV circuits to share a neutral (particularly interesting if the ELV were DC), wouildn't it?

Kind Regards, John

 

[ban-all-sheds]

You'd have to keep the pilot circuit completely separate, not linked to the LV N at the equipment end.

Mixing wouldn't be a problem because plug, socket and cable are all insulated for the highest voltage present.

 

[JohnW2]

You'd have to keep the pilot circuit completely separate, not linked to the LV N at the equipment end.

I don't think you could without a second pilot pin, could you? You cannot create a circuit without some return path, hence my comment that Bernard's idea would require sharing of the neutral.

Kind Regards, John

 

[SimonH2]

You'd have to keep the pilot circuit completely separate, not linked to the LV N at the equipment end.

And how do you propose to do that with one pilot pin ?

Linking it to <some pin> at the load side, and running an ELV circuit at the supply side to control a supply switch would make sense. It wouldn't matter about making the pilot pin live either - it's recessed in the socket so no more dangerous than any other pin.

I always assumed that the intention wasn't to remove voltage from an unmated socket, rather to remove the ability to make/break a heavy load. If used for earth monitoring, the obvious question might be what benefit that provides on a 63A or larger circuit, which wouldn't also be the same benefit on a smaller size ? Ie, once above 30mA, it doesn't really make much difference what the current capacity of the supply is when determining how hazardous a lost earth is.

But of course, I find myself wondering if there are any special cables with a small core for the pilot circuit - or do people spend a lot of money on providing an oversized (same as the rest) conductor for it ?

 

[SimonH2]

... the arrangement you described would requite the ELV and LV circuits to share a neutral (particularly interesting if the ELV were DC), wouildn't it?

I don't see that as any great problem - whether AC or DC. However whatever circuit was used would need to allow for the possibility of losing the neutral and imposing up to the full line voltage onto the circuit. Not hard, as long as it's considered at the design stage.

 

[JohnW2]

... the arrangement you described would requite the ELV and LV circuits to share a neutral (particularly interesting if the ELV were DC), wouildn't it?

I don't see that as any great problem - whether AC or DC. However whatever circuit was used would need to allow for the possibility of losing the neutral and imposing up to the full line voltage onto the circuit. Not hard, as long as it's considered at the design stage.

Electrically-speaking, I agree with you (although 'allowing for that possibility' might not be so trivial). However, I'd have to study the regs to see what they've got to say about two different 'supplies', at different voltages, sharing a conductor, particularly if one is AC and the other DC!!

Kind Regards, John

 

[bernardgreen]

I can see no problem with a ELV control voltage having one side connected to and using the neutral conductors. If the control voltage was 230 volt the question wouldn't arise.

It has the advantage that the voltage on control panel switches and lamps will be limited to the ELV control voltage above ground ( assuming neutral and ground are tied together ) hence little if any hazard to operators using the panel.