Pilot pin on 63A BS4343 connectors

[ban-all-sheds]

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

With magic, of course.

 

[AdrianUK]

The 'correct' (well, the BBC interpretation of it) implementation of the pilot pin was for earth monitoring.

The pilot pin would be independently connected to the chassis at the 'appliance' end via a pilot core in the cable (usually around 2.5mm sq). This would form a loop between the earth pin & the pilot pin. In the socket a transformer was used to derive an isolated supply which would be connected to the earth pin & the pilot pin via the coil of a contactor. Thus when a plug was inserted a small current could flow around the loop, pulling in the contactor and energising the main circuit. Should the continuity of the earth path between the 'appliance' and the socket be lost, the contactor would drop out.

 

[Lectrician]

That's how I have always heard it to be used, using a 24v AC source.

 

[SimonH2]

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.

Not so.
Suppose there is a neutral fault anywhere between where the pilot circuit is connected to it at both ends - certainly you can't rule out a connection coming loose in a plug or socket, or a pin "burning out". You now have current flowing in line out, attempts to return via neutral, but since that is broken then you'll impress line voltage on the pilot circuit. So back at the supply end, you've a circuit tied to supply neutral, and with supply line on it's other side. Since we're talking 63A and above, we can assume connected loads may be of fairly low impedance.

So our pilot circuit must cope with line voltage imposed on it - with (for practical purposes) potentially very little by way of current limiting, and no effective overcurrent protection.
That's not too hard to design for, but you certainly cannot say that the pilot circuit is ELV.


Such an innocent initial question, such a long (and interesting) discussion !

 

[bernardgreen]

Suppose there is a neutral fault anywhere between where the pilot circuit is connected to it at both ends - certainly you can't rule out a connection coming loose in a plug or socket,

This is a hazard, the risk has to be calculated for each instal. If the ELV is sourced in the control panel and one side of the source is connected to the neutral at the control panel then the risk is the same as the risk from the loss of the neutral supplying a PME domestic install. But in an industrial install the earth and neutral seldom share the same conductor so the panel will remained earthed even if its neutral is lost. Loss of the neutral to the control panel will ( should ) activate automatic protection and/or invoke operator procedures to ensure safety is not compromised.

 

[SimonH2]

Loss of the neutral to the control panel will ( should ) activate automatic protection and/or invoke operator procedures to ensure safety is not compromised.

Yes, but you said that by using an ELV pilot circuit, all the switches/indicators would only be ELV. What you've written is correct, but doesn't change the fact that the pilot circuit can be energised to line voltage should there be a neutral fault downstream of the switching panel and upstream of where the pilot circuit links to neutral in the powered equipment.

To ensure the switches/indicators are ELV, you would need to run them from a separate ELV supply from that supplying the pilot circuit, and isolate the control circuits from the pilot circuits (eg with a relay).

Whatever, as long as the system is designed to take care of this possibility, then there should be no hazard to any operator.