Control Panel Isolation question

[TailSpin]

:banghead:Hi all

Just a question on isolation on a control panel which has contactor and overload set up for a small pump.
When the main isolator is off parts of the auxilary side of the overload was found to be still live from another source.

Would this be covered by BS7671 or are there other BS to consider ?

Regards
John

 

[davesparks]

Bs7671 only really covers the supply up to the panel isolator, after that you are in to the specific regulations governing panel building. Supplies from other sources are normal for interaction/interlocking with other panels, signalling, essential supplies (panel lights and heaters etc) but these should follow a specific colour code for ease of identification.

 

[Darkwood]

It comes under the LV Directive possibly BS 60204.. cannot say anymore for the limited info you have given but there are regulations that govern all these systems, are you sure this isn't just a local means of isolation for the motor and the whole pump control and power don't come from a larger system that would isolate all supplies if powered down.

What is your interation with this system? .. this will be out of the scope of the general training of an Electrician and more so for an Electrical Engineer who is fluent in the relative regulations, be very careful if getting involved in such work as your keen testing has shown, in this area of work been unsure can be costly if not from a financial context then a safety point of view.

 

[snowhead]

I've worked on many panels over the years.
It's not uncommon to have supplies from multiple sources, not isolated by the main panel isolator.
Usually there will be a warning notice.
Also quite common it to have supplies to maintenance sockets, lights and BMS controllers not isolated by the panel main switch and fed from the live side of the isolator,

Simple rule for working in control panels, Beware anything may still be live AND / OR may become live whilst the panel is open.

 

[Darkwood]

Also to add - test sequences can differ and a knowledge of the control voltages is also essential.

AC / DC
Isolated TX control with varying output set-up be it earth free, one leg strapped down or centre tap and even more dangerous are poorly installed equipment that may have a 0-10v control signal but actually can possess a floating voltage of 230v to earth (seen this a few times espescially with DC drive cards not having the speed pots running through a galvanic isolation device when required).

I've seen people test for voltages with multimeters set on AC and then think its safe to work on just because they never needed the DC setting before.