three phase and earth fault protection

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How is earth fault protection provided on a three phase board, debate amonst subbies on site, no single phase circuits, and a 60973 main switch
Dev
 
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tri phase mccb's do not provide earth fault protection, as do rcbos' an rcd is required but where is it to be installed, at origin of supply apparantly not So if a tri phase is installed to prvide a supply to one three phase circuit where's the protection ?
 
tri phase mccb's do not provide earth fault protection, as do rcbos' an rcd is required but where is it to be installed, at origin of supply apparantly not So if a tri phase is installed to prvide a supply to one three phase circuit where's the protection ?

So install one with adjustable earth fault protection.
 
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BSBS, they do not refer to those as (RCD's) rather adjustable thermal protection is this the same and can you tell me a make (not proteus)
Dev
 
What are you on about?

If you got a fault to earth it will operate the overcurrent protective device for that phase or for the entire circuit if it's a TP MCB.

Are you asking about providing RCD protection to a TP circuit, or a TP installation, or something completely different?
 
Ok why have rcd at all, at present we must have efp and ocp on single phase why does the same not apply to 3 phase a 3 phase MCCB does not have efc prtotection, over load only, yes I know it amounts to the same thing (automatic disconnection) wether its a short circuit or a fault to earth We have just installed a new 3 phase board all new moulded case circuit breakers (new name for mcb's with a new price to match) main switch is bog standard 3 pole iso so where is the requirement for efp or does the fact that all circuits are dedicated supplies to various machines negate this requirement, hope this is clear enough.
Devlin
 
I think I understand what youre getting at.

You do NOT need to RCD protect all single phase circuits.

In a standard domestic premisis the easiest way to comply with BS7671 is to RCD protect most or all circuits.

In a commercial or industrial environment it is unlikely that all circuits will require RCD protection, and often the only place an RCD is required is to protect a final circuit supplying 13A sockets for general use, and other circuits which have been identified as presenting more risk to the users.

You would never RCD protect a submains, as a cleaner plugging in a faulty vacuum could take out half the factory for example.

RCDs do not discriminate like OCPDs do.

Do you understand the difference between overcurrent protection and earth fault protection and why they are provided, or even what the difference is between the types of fault?

I'm not having a go, but understanding this will greatly help you understand where and when you would use each type of protection.

MCCB is not not the new name for MCBs.

MCB is an incorrect name for a circuit breaker.

An MCCB is not the same as a circuit breaker.
 
Perhaps you can tell me am I wrong overcurrent is L_N fault in an ok circuit and a L_E is a fault to earth,and what then is a mccb or a mcb as I understand it a mcb is a generic term for a circuit breaker and a mccb is now been given over to mean a moulded case circuit breaker But again this could be the industry jazzing up the handouts But what I was on about was the 3 phase rcbo's I have never seen one in a board ever if they are need what would be the circumstances for that.sorry if it sounds drivel it's been a long day and I have been up and down ladders,lofts, all fizzin day
 
Overcurrent is basically what it says, any condition which causes more than the design current to flow in the circuit, this can be caused by overload or a fault condition

Faults can either be:

A) Phase ->Neutral or Phase ->Phase (termed a short circuit)
B) One or many phases to earth (termed an earth fault)

An MCB is a minuture circuit breaker as defined in BS3871, BSEN60898 does not refer to them as such; prefering to apply the name 'circuit breaker', but the term MCB is still widely used as it makes it clear you are taking about devices to fit in a final distrubution board

MCCB is as you quite rightly point out is 'moulded case circuit breaker' and are the devices to BSEN 60947-2 used in panel boards...

Both MCBS (or CBs if you want to be technically correct ;) and MCCBs can protect against all the above types of fault if the design is carried out to make use of their characteristics.

Earth leakage shunt trip units are available for MCCBS, but the situations that require them are not that common, larger supplies are most often TN systems, and if Ze is a little high, then careful design of the installation should allow the avoidance of earth leakage protection at this level of distribution
 

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