Rank: New forum user 
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I was asked if locking out the supply to a contactor coil be classed as safely isolating an electrical supply to allow work to be done?
I dont think it does as the contactor springs could fail and close, it could arc if insufficient coil gap due to faults or carbon build up, the air gap (3mm) is unknown and in some cases it is possible to manually close the contacts therefore I would not regard this as suitabley isolated.
Any coments?
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Rank: Super forum user
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No point in not using caution if there is a risk of arcing across there.
Some of the older types of MCB's can be just as you suggest, especially if there is significant disturbance of debris, dust etc.
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Rank: Super forum user
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The only safe way of isolating the power is to open a switch designed for that purpose and ensure the switch cannot be close accidentally. This can be achieved by taking the main fuse or MCB out of the system or disconnec ting the supply cable therefore making the circuit dead. That is the only safe way of doing it in my view.
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Rank: Super forum user 
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McElroy16995,
IMHO no a contactor alone cannot be used for safe isolation.
However, BS7671 now allows several other devices to be utilised and a suitable contactor is one of them. To be suitable it must be marked with the specific symbol for isolation.
Your MS would need to consider inadvertant energising of the contactor.
I don't have the detail to hand, but I suspect if a contactor is suitable for safe isolation it would have the ability to be locked in the open position, I have seen such devices.
Locking out the control supply only again IMHO would not be acceptable.
The chances of a fully de-energised contactor arcing or inadvertantly closing are extemely remote I would say.
I have to presume you are talking about low voltage supplies?
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