MCB type and current rating. Who knows their stuff?!

alphonse mephisto

Being tested on the wiring and testing of a commercial electrical installation. So far it is going very well as you would expect, im as far as wiring the distribution board now and there are a few things Ive started to second guess myself on. Everything has to be in line with the current ETCI regs. Please let me know if RCD or mains power is required. Once again i know how I would do it but I need to be completely sure! Each appliance will be on its own dedicated circuit.

I need to know the correct type and size of protection for:

1.5Kw undersink water heater

2Kw Burco boiler

1.5Kw hand dryer

1Kw 3phase gas heater

Fire alarm panel, will i put this on the mains power? It makes sense for this not to be on a common RCD but should I put it on a RCBO or will the DC mess with it?

16amp single phase industrial socket

16amp 3phase industrial socket

One last thing, for an IT clean supply am I correct in thinking that I can put these sockets on the mains supply as long as the out let is non-standard and labeled? Will this achieve a clean supply?

Any help here would be greatly appreciated! Thanks!

M cebee

what do you think?

2011

No offense intended, but you are out of your depth here. This type of work should only be carried out by a qualified electrician. Sometimes a little knowledge can be a very dangerous thing.

The best course of action is to employ a registered electrical contractor.

Bruthal

I though he was asking in terms of an exam for some reason.

2011

robbie7730 wrote: »

I though he was asking in terms of an exam for some reason.

Oops! Looks like you might be correct

Apologies OP, provide your best guess and someone here will assist.

Bruthal

2011 wrote: »

Oops! Looks like you might be correct

Apologies OP, provide your best guess and someone here will assist.

I only quickly read it yesterday myself.

alphonse mephisto

1.5Kw undersink water heater: Wired in 2.5 t+e on a 20amp type b on rcd connected through switched fused spur unit.

2Kw Burco boiler: Wired in 2.5 t+e on a 20amp type b on rcd connected through switched fused spur unit.

1.5Kw hand dryer: Wired in 2.5 t+e on a 20amp type b on rcd connected through switched fused spur unit.

1Kw 3phase gas heater: Wired in 1.5nymj on a 10amp type c on mains connected through 3phase isolator.

Fire alarm panel: Wired in 2.5 t+e on a 20amp type b on mains connected through unswitched fused spur unit.

16amp single phase industrial socket: wired in 2.5nymj on 20amp type c rcbo

16amp 3phase industrial socket: wired in 2.5nymj on 20amp type c and 3phase rcd connected through 3 phase isolator

clean IT supply: wired in 2.5t+e 20amp type b without rcd

1.25Kw convection heater: wired in 2.5t+e on 20amp type b with rcd connected through switched fused spur unit.

There is an awful lot more in the test that im completely fine with, just after i handed in the portfolio the tester said that it was grand but that all the information wasnt 'necessarily correct'. I wouldnt really ask otherwise.

2011

alphonse mephisto wrote: »

1.5Kw undersink water heater: Wired in 2.5 t+e on a 20amp type b on rcd connected through switched fused spur unit.

2Kw Burco boiler: Wired in 2.5 t+e on a 20amp type b on rcd connected through switched fused spur unit.

1.5Kw hand dryer: Wired in 2.5 t+e on a 20amp type b on rcd connected through switched fused spur unit.

1Kw 3phase gas heater: Wired in 1.5nymj on a 10amp type c on mains connected through 3phase isolator.

Fire alarm panel: Wired in 2.5 t+e on a 20amp type b on mains connected through unswitched fused spur unit.

16amp single phase industrial socket: wired in 2.5nymj on 20amp type c rcbo

16amp 3phase industrial socket: wired in 2.5nymj on 20amp type c and 3phase rcd connected through 3 phase isolator

clean IT supply: wired in 2.5t+e 20amp type b without rcd

1.25Kw convection heater: wired in 2.5t+e on 20amp type b with rcd connected through switched fused spur unit.

There is an awful lot more in the test that im completely fine with, just after i handed in the portfolio the tester said that it was grand but that all the information wasnt 'necessarily correct'. I wouldnt really ask otherwise.

Looks good, just a few comments:

1) Normally for the above on an industrial installation I would specify that everything would use type C MCBs. Typically I would cable the circuits such that the CPC is the same size as the phase conductor. However there is nothing wrong with what you have done.

2) I would always use RCBOs where ever possible. They are neater, take up less space and there is less connecting.

3) Clean IT supply, I would state that non-standard sockets are used.

4) Hand dryer, I would use an unswitched spur outlet as I don't like switches near wet hands. I know some will disagree, but that is me.

5) Normally in industrial/commercial installations we would specify a 4 sq. mm cable at a minimum for 16A single or 3ph socket outlet.

M cebee

yes his answers look good to me

-I'd be looking at fitting all C type as well

-16amp mcbs for 16amp sockets imo

-as you say all the appliances seem to be 13amp so c20 mcb+rcd or rcbo and spur

-fire panel no rcd,unswitched spur+neon

-hand dryer-switch spur at high level seems to be the norm-does that comply now?

-clean line-either mcb to non standard socket
or type A rcd to standard 13amp socket

-mcb and isolator for gas heater

all rcbo's is preferable for the 13 amp appliances,there's a couple of water heaters in it

and confirm manuf instructions on fusing

alphonse mephisto

Alright grand,

Its a mixture of warehouse, canteen and offices and thats why I have different types of mcb's. All the type c's are supplying the warehouse circuits.

The clean IT supply will will be non-standard and labelled, think I stated that in the first post... And the DB I was supplied with for the test is 3x26 way and its looking like it will be fairly full otherwise I would be using alot of rcbo's.

One last thing, I do feel similar on your fourth point but the regs say that all fixed appliances must be provided with a means of isolation, hence the switched spur.

The test itself hasnt got a percentage whereby you pass or fail, everything just has to be in line with the regs and industry standard or you fail. Its a good test and the tester wont confirm or deny anything. Its a good challenge.

2011

alphonse mephisto wrote: »

Alright grand,

Its a mixture of warehouse, canteen and offices and thats why I have different types of mcb's. All the type c's are supplying the warehouse circuits.

Fair enough, but this would not be the industry norm.

The clean IT supply will will be non-standard and labelled, think I stated that in the first post... And the DB I was supplied with for the test is 3x26 way and its looking like it will be fairly full otherwise I would be using alot of rcbo's.

A minimum of 25% spare capacity for future use would be typical.

One last thing, I do feel similar on your fourth point but the regs say that all fixed appliances must be provided with a means of isolation, hence the switched spur.

That is why I said that some would disagree. The spur with neon (I like neon indication, quick for fault finding) could be installed local to the hand dryer with a DP 20A isolator at high level.

The test itself hasnt got a percentage whereby you pass or fail, everything just has to be in line with the regs and industry standard or you fail. Its a good test and the tester wont confirm or deny anything. Its a good challenge.

What is the test?

Good luck with it.

alphonse mephisto

As it is offices and canteen and not just warehouse would you recommend that I supply the offices and canteen with type c? The other limitation is that we are supplied with no type A mcbs, alot of type b and very few type c so this would seem unlikely to me that the testers want to see this?

M cebee wrote: »

yes his answers look good to me

-I'd be looking at fitting all C type

-16amp mcbs for 16amp sockets imo

-as you say all the appliances seem to be 13amp so c20 mcb+rcd or rcbo and spur

-fire panel no rcd,unswitched spur+neon

-hand dryer-switch spur at high level seems to be the norm-does that comply now?

-clean line-either mcb to non standard socket
or type A rcd to standard 13amp socket

Bruthal

M cebee wrote: »

-16amp mcbs for 16amp sockets imo

Id probably prefer 20 myself. Gives a little extra for welder surges and that sort of thing. Probably not a big factor though.

alphonse mephisto

Ok grand, any and all ideas are helpful! Thanks.

Its called competency determination. Its a fas thing. Ive been at this 10 years and aced all their tests but still dont want to give the cert!

Its funny though, they say it has to be in line with the regs but want me to ignore things like the emergency stop on the motor control circuit.

alphonse mephisto

robbie7730 wrote: »

Id probably prefer 20 myself. Gives a little extra for welder surges and that sort of thing. Probably not a big factor though.

I would tend to agree with you on that... Either way they dont supply 16amp type c!

alphonse mephisto

One last thing, A 6amp type b would be fine to supply my emergency lighting test panel? Correct? I can put it on 10amp of course but if it doesnt need it whats the point?!

Bruthal

2011 wrote: »

2) I would always use RCBOs where ever possible. They are neater, take up less space and there is less connecting.

Without all the other advantages, the easier connecting alone makes them much better.

4) Hand dryer, I would use an unswitched spur outlet as I don't like switches near wet hands. I know some will disagree, but that is me.

Back to semi-skilled work for you, with suggestions like this....:D
Only joking, Id agree really.

Bruthal

alphonse mephisto wrote: »

One last thing, A 6amp type b would be fine to supply my emergency lighting test panel? Correct? I can put it on 10amp of course but if it doesnt need it whats the point?!

Should`t be any problem with the 6a b

M cebee

robbie7730 wrote: »

Without all the other advantages, the easier connecting alone makes them much better.



Back to semi-skilled work for you, with suggestions like this....:D
Only joking, Id agree really.

I've had to replace some lately
prefer the switched spur at high level and flex outlet at dryer meself
-not sure either method actually complies with isolator 4-1600 height rule

M cebee

the burco boiler and other commercial equipment thay may be supplied with plugs-i wouldn't be cutting them off these days

may not be an issue in this test

liveandnetural

dont foget that cable lenght and type has a effect on earth loop impedance so it will influence the trip times (so saying use all c type may not always apply)

http://www.voltimum.co.uk/news/1826/cm/selecting-the-right-mcb

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its-as-easy-as-bcd-.html

2011

liveandnetural wrote: »

dont foget that cable lenght and type has a effect on earth loop impedance so it will influence the trip times (so saying use all c type may not always apply)

I disagree, deliberately mixing B and C type MCBs is not normal practice in this type of installation. They may end up that way after several years, but that is not the original design intent.

Normally on industrial installations type C MCBs are used for all of the circuit types listed by the OP. If necessary cable sizes are increased for longer cable runs to ensure that the volt drop is not excessive and the required disconnection times are met. Phase and CPC conductor sizes are typically the same size in this type of installation nowadays which also reduces EFLI values.

M cebee

a 'c' type board and rcbo,mcb mix is the correct way imo
-efli values should normally be within limits ime
-on larger jobs i imagine calculations are done for dist. circuits and final circuits to ensure tolerance

2011

M cebee wrote: »

-on larger jobs i imagine calculations are done for dist. circuits and final circuits to ensure tolerance

Frequently on large projects a "worst case" example is calculated to demonstrate that chosen cable and protective devices comply. Once this has been demonstrated all similar circuits can then use the same cable and MCB.

frankmul

2011 wrote: »

Normally on industrial installations type C MCBs are used for all of the circuit types listed by the OP.

is the MCB sized according to the size of load and the type picked to suit the type of load regardless of location of the board.
B for resistive
C for inductive
D for highly inductive
are D's allowed on circuits other that trafos now?

2011

frankmul wrote: »

is the MCB sized according to the size of load and the type picked to suit the type of load regardless of location of the board.

Agreed, nobody suggested otherwise.

B for resistive
C for inductive

This is simply incorrect.

Type D are commonly used for transformers.

2011

Here is a good link explaining the differences.

Type B trips between 3 and 5 time full load current;
Type C trips between 5 and 10 times full load current; and
Type D trips between 10 and 20 times full load current.

frankmul wrote: »

are D's allowed on circuits other that trafos now?

What is important is that the minimum disconnection times are achieved.
This means that a lower earth fault loop impedance is required for a D type than a C and a lower value is required for the C than the B (with everything else remaining equal)

frankmul

2011 wrote: »

This is simply incorrect.

I'm not sure what you mean by incorrect, I meant type b is used for resistive loads where there is not switching surges, typical of domestic installations but they can also be found in commercial and industrial.
I know that once you get your earth fault loop impedance low enough, you circuit will trip within the max time allowed but what about discrimination between devices

Bruthal

Type b will do inductive loads too. Not everything in a house is resistive.

frankmul

I agree there is loads of inductive loads, Freezer, pump, fridge. Type b handle these perfectly

frankmul

robbie7730 wrote: »

Type b will do inductive loads too. Not everything in a house is resistive.

I agree, fridges, freezer, pump, fluorescence light. Type b will do for these loads