Ross Trician

Hello chaps,
Can any of you either tell me or point me in the direction as to what the rules/regs are with regards to voltages used for control circuits.

I am asking because we have been having dicussions about wether you need to use low voltage, ie24V instead of 240V for control circuits, i.e stop/starts etc.

Do any of you know of any good book that provide information on design and construction of electrical panels etc with reference to the regs.

any help appreciated.

thanks Ross.

wayne

never come across regs regarding control voltage other than those which relate to selv/pelv/class1 class two but then i might have missed
never had an issue using 230 volts on em stop circuits used in say a classroom
i believe it comes down to control panel design and some of the things you need to look at are;
other voltages present and are you insulated to highest present
what instrumentation cable is inside the panel
length of run
type and voltage of other instrumentation present
am i on the right lines?

Ross Trician

Hello wayne, thanks for the reply.
I work in a factory and it is something that we in the engineering department have spoke about on several occaisions.

We have some of the panels which have 240v control but as a rule we make new instalations 24v where possible. we have to deal with quite a few numpties who have no regard for the stuff they are working with. also we have a quite wet enviroment at times as there is a dedicated hygene team who try to wash the world away, lol.

we dont tend to have any instrumentation etc on the factory floor it is mainly stop/start/e.stop/reset type stuff.

wayne

ive done panel building before maybe theres a designer out there who can take this further ill add more as it comes to me

wayne

to add further ,the regs concern themselves with installations rather than panel building

Shakey

Agree with Wayne

I am not aware of any regs that govern this, but obviously, the lower the voltage the better. even if a control circuit requires 230V, that can be controlled through 24V using relays

mattyfooty

There are no Regs that I am aware of concerning control panels, but 24v seems to be industry standard. One advantage I do know is that a control panel/circuits that are designed for 24v do not need a Ce mark which gives a lot more freedom on design.

treelectric

As far as I know you are right about no regulations, but there are industry standards covering this, and as you point out, the the overall wiring standards are much less rigorous when you bring 24v out of the control panel to micro switches, etc. The accepted industry standard is now that 'simple' starters can operate with phase voltage to the coil, including 400 volts, but it must not come forward to any push buttons. The push buttons just operate directly on the aux contact of the starting contactor and the overload trip button via plastic rods.
Once you get 2 or more contactors operating with wired buttons it is no longer 'simple', and the accepted industry standard is now 24v. It's usually ac if contactors are involved, because large dc coils have to be suppressed to protect the operating switches against arcing causing premature failure of contacts. While I've been involved in control panel design, (over 30 years), the control voltage standard has gone from 415 volts, to 240 volts, then 110 volts, and now 24 volts ac. 24v dc is still used on banks of small relays, but even here there is still the extra work needed for coil suppression if there is any computer control or plc's in the system, so 24v ac is becoming the norm. Hope this helps.
PS some companies, pepsi cola being one that I know of, actually specify their own unique standards. The sooner we get the equivalent to BS7671 in this area the easier it will be for all.

rumrunner

exellent answer!

wayne

seeee i told you there was a panel designer out there and now we're all wiser