BS7671 537.2.5

Question

Question can you lock and isolator ON? 
 from 537.2.5 it says an off load isolator can be locked on. 
 A designer is saying to me you can use an onload device (it s a rail application), but to me it clearly staes it has to be an off load device. 
 
 Any thoughts?

mapj1 · Accepted Answer

Given that an 'off load' isolator should only actually be switched from on to off once the current has already fallen to zero due, presumably, to switching elsewhere, it is not unreasonable that in some cases someone may want a lock to prevent it being turned off accidentally. Though I cant think of a real example off hand... Equally all sorts of switch gear is commonly locked to prevent operation at the wrong time by the wrong person, if need be by the use of locked doors on the switch room, so there is always that more general way of doing it. Mike.

gkenyon · Answer

Alex Cooper said: I need to add they they are proposing to use an on load isolater and padlock it on. 
 Here is an example, from the IET Electrician's Guide to Fire Detection and Fire Alarm Systems , 3rd Edition, that clearly shows that, not only is locking isolators in the 'on' position an accepted practice, but more importantly that it is actually required in some cases:

BS7671 537.2.5

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