3 phase questions for the sparkys.

[scott0031]

I'm having to take a look at my 3 phase supply due to the insurance co being normal a_ _ holes that they are. Naturally they are demanding certification of said wiring.

Upon getting one quote from an electrician, which incidentally nearly cut my life very short indeed, I had to seriously question what the hell he was going to do for that amount of money.

My distribution board is an old crabtree with C50 mcb's. I automatically assumed this would have to be replaced due to its age. A bit further investigation it seems this may not be the case at all, providing the mcb's meet the trip times they should meet. If the mcb's meet the criteria, the way im seeing this is the only thing i need to actually do is add 4 pole RCD before the incomer. Could one of you kind gents please confirm.

I installed the whole 3 phase in the building about 8 years ago now. What i did not do was install a neutral throughout system beyond the dist board. Purely for the fact that nothing i have 3 phase needs a neutral and is not wired for it from the factory, what is the score do i need to have a neutral system in place to meet regulations, even though its of no use at all.


Many thanks in advance.


Kind regards,


Scott

 

[madkayaker]

on three phase there is very little requirement for a RCD as the regs work on the basis that three phase is industrial therefore a risk assessment would determine whether a RCD was required. if its feeding fixed bits of kit then i wouldn't normally RCD providing that the trip times are met (can be very hard to get C and D types to meet due to the very low ZS values). there is no requirement to install N unless its needed by the equipment.

 

[Drains]

MK, as welding plant is seldom fixed, would that suggest an RCD should be in place, or would the MCBs suffice?

I guess with the trip time issue too the answer is no, and an RCD would be needed.

 

[madkayaker]

i wouldn't insist on a RCD for a dedicated supply to a welder or any other machine if its plugged in inside a workshop however if there was to be extension leads of kit to be dragged outside/ near the door i would RCD those sockets. welders are low risk pieces of kit imho as the output side is isolated from earth and is reduced voltage

 

[scott0031]

on three phase there is very little requirement for a RCD as the regs work on the basis that three phase is industrial therefore a risk assessment would determine whether a RCD was required. if its feeding fixed bits of kit then i wouldn't normally RCD providing that the trip times are met (can be very hard to get C and D types to meet due to the very low ZS values). there is no requirement to install N unless its needed by the equipment.

Thank you madkayaker, that's some interesting info there. I think i can see where conflicting views or what is/is not required come into play with the individual electrician depending if they are giving unbiased advice or quoting the job. in my case.

I would guess a risk assessment is open to much interpretation again depending who is doing it. Although you say you would not normally rcd the 3 phase input with fixed installations (which mine is). What if those mcb's the C and D( higher initial loads types) do not meet the trip time, as you mention they very often don't, so does that mean you have to rcd due the the mcb failure to comply?

Am i misunderstanding something here?


Also does the fact i run sockets out of my isolators effect the viewpoint if rcd protection is needed? In short what i have is this: Dist board > isolator > Sockets 16 or 32 amp. Most of my equip is plugged in for versatility although its stationary kit, mills lathes etc. Although still stationary, i do have a few things like a belt grinder and a polisher which can be moved in the technical sense, does this mean this Auto qualifies for it to be rcd'ed even though it does remain stationary?


Again many thanks indeed.


Kind regards,


Scott

 

[awemawson]

When I installed my 3 phase - (which is a biggish system with a 160 amp incomer) I took the view that as it would be my life I'm protecting each distribution board would have a 30mA RCD, not the more usual 100mA as per industrial practise. I reckon if my leakage gets near the 30mA level I need to sort it! The other reason is that some machine have 13a sockets for ancillaries such as lights and pumps using phase 1 and neutral, and with the main rcd EVERYTHING was covered.

 

[madkayaker]

I would guess a risk assessment is open to much interpretation again depending who is doing it.

the regs are only the MIN standard if you feel thats it approperate to apply more safety then do it!

Although you say you would not normally rcd the 3 phase input with fixed installations (which mine is). What if those mcb's the C and D( higher initial loads types) do not meet the trip time, as you mention they very often don't, so does that mean you have to rcd due the the mcb failure to comply?

yes

Am i misunderstanding something here?


Also does the fact i run sockets out of my isolators effect the viewpoint if rcd protection is needed? In short what i have is this: Dist board > isolator > Sockets 16 or 32 amp. Most of my equip is plugged in for versatility although its stationary kit, mills lathes etc. Although still stationary, i do have a few things like a belt grinder and a polisher which can be moved in the technical sense, does this mean this Auto qualifies for it to be rcd'ed even though it does remain stationary?

you have to consider the risk that you feel is posed by the electricity jumping out of the cable and getting you! . the regs are written for every installation under the sun and its up to the tester, installer and user to decide what is appropriate. i would as a matter of corse RCD any 230V sockets as they might be used for hand tools and any 400V that could be used for extension leads or to run kit outside. a socket that is going to feed a machine is very low risk providing the machinary is suitable maintained, Regulation 16 of electricity at work regs states that suitable and adequate maintenance shall be carried out by competent persons to ensure as far as is reasonably practicable agents electric shock (might not be those exact words but you get the gist!) what is deamed as reasonable and competent will only be tested after someone has had the wiggle knocked out of them and someone is in court!

Again many thanks indeed.


Kind regards,


Scott[/QUOTE]

 

[madkayaker]

When I installed my 3 phase - (which is a biggish system with a 160 amp incomer) I took the view that as it would be my life I'm protecting each distribution board would have a 30mA RCD, not the more usual 100mA as per industrial practise. I reckon if my leakage gets near the 30mA level I need to sort it! The other reason is that some machine have 13a sockets for ancillaries such as lights and pumps using phase 1 and neutral, and with the main rcd EVERYTHING was covered.

teats a good way of doing it but motors and transformers can be leakey. at work our N-E alarm is set for 25A but we take off the grid at 11kv and can pull 6mW but we do get alarm from time to time (suspect is a ups)

 

[scott0031]

Thank you very much madkayaker. Very helpful indeed.


I do get the jist the way the regs work, which i guess knowing this country the EU etc its no surprise at all / Make a rule/statement, don't clarify it beyond doubt. Good way to keep there mates in the legal system busy i guess Hey ho.


Thank you again,


Kind regards,


Scott

 

[madkayaker]

thats the jist just enough wiggle room to hang yourself!

 

[Wedg1e]

we take off the grid at 11kv and can pull 6mW

Six milliWatts? That's not much!

 

[madkayaker]

sorry megger whatt

 

[Shox Dr]

sorry megger whatt

It's not your day is it MK

I'm sure you meant; Megawatt

 

[madkayaker]

i know what i meen! its not my fault im special......

 

[scott0031]

Sorry to resurrect this thread sparkys but more questions!


I mentioned that in the main i use 3 phase sockets below isolators which i plug equip into, one set of these sockets is used for my welders. I also plug other equip in these sockets, like a belt grinder, polisher and a mill when the need arises.

I'm struggling to get an answer which mcb type i should be using for this circuit should i be using a C or D type? obviously each type does a different job so can a C be used with welders or will it trip? I do have an electrician overseeing the work , but he did seem a bit non committal of which mcb type i should be using and which will work for all my uses. I should mention all my welders are transformer.


Second question, I have been told i have to renew the lighting in my works, so i have new lights sitting in their boxes. I have been told these new lights have to be fitted to the ceiling of the building as apposed to being suspended as they are now. OK that's fine but in this case it seems unwise to me as the building is lined with 4 " of cork. 1) fire risk if said lights develop a problem. 2) This cork is not the best condition and does de-laminate in time which means the lighting will be, well a mess and have to be redone at some point. It seems to me suspended is a better option and safer. Where do i stand with this?


Many thanks indeed,


Scott

 

[madkayaker]

C or D type will be decided by the ZE and ZS you have. if you can fit D for the welders as C will give you some nucence triping. but if the ZS is going to be to high then you will have to use C or add RCD's to the circuits then you will get diconection.

not quite sure what you meen with the lighting but fittings will say if there suitab le for mounting on flamible surface

 

[HOUNDMAGNET]

Hi,as for the type of mcb to use,these are the recommended uses.

C - Normal inductive loads - smaller motors, flourescent lighting (switched together in large banks) and some domestic circuits where there is an initial inrush.
D - Heavily inductive loads - used with larger motors started by conventional means (direct on line or star-delta

Type C - trips between 5 and 10 times full load current

Type D - trips between 10 and 20 times full load current


so i would use a D type, but only if the zs is low enough.If you have an electrician doing this work,then he is responsible as it is he who signs off the work.If you give him a stated design,and he doesnt agree to it with regard to safety and regulations,then he cant sign it off...simples


As for your lights.Who says they cant be suspended?

And as above,it is up to the electrician to determine if the enviroment is suitable for them to be fixed..if it isnt,then he shouldnt do the work.By the sound of it the fittings will need to be suitable for use on a flamable surface,and you may need to use fire proof cable as well.
I cant remember the actual regulation number regarding this,but there is one

 

[scott0031]

Many thanks Gents. The information on the MCB'S very useful indeed to allow me to understand it myself. D it is


The light problem was due to the light fittings/cables being able to swing and chaff, my reply was well stick a grommet it in! Then i was told well ya cant have an exposed cable hanging down etc etc.. But that said today i have clarified it and they are totally agreeable to have them hanging as before, which is a lot less work as chains are already in place, especially when trying to fix to cork.


Many, many thanks gents.


Kind regards,

Scott