What type of circuit breaker would be used for a three phase circuit?

[WilliamAtkin]

Hi ,
Currently doing a design project in college and I need to pick a circuit breaker ( In device rating and type) for a food holding equipment unit that requires a 16A 400V three phase and neutral supply that is supplied by 5 core SWA. I think I should pick a 16A 3P+N RCBO but wasn't completely sure so thought I would run it by on here 1st before I write anything down.

 

[James]

What is the reasoning or requirement for an rcd?
It is also, unusual but not unheard of to have 4 pole circuit breakers for 3 phase equipment.

 

[WilliamAtkin]

What is the reasoning or requirement for an rcd?
It is also, unusual but not unheard of to have 4 pole circuit breakers for 3 phase equipment.

well doesn't that circuit need to be protected like all the other circuits which are all rcbos so I thought it would be best for this to be a rcbo instead of a 3P+N MCB with a RCD. But am I right to use a 3P+N breaker for 3 phase though ?

 

[westward10]

Is the food holding equipment connected by way of a socket outlet, if so the rcd can be incorporated into the socket outlet. If not and fault protection is afforded by the mcb then rcd protection is not required unless manufacturer instructions suggest it and this must be taken into consideration.

 

[davesparks]

well doesn't that circuit need to be protected like all the other circuits which are all rcbos so I thought it would be best for this to be a rcbo instead of a 3P+N MCB with a RCD. But am I right to use a 3P+N breaker for 3 phase though ?

You can't design an electrical installation by assumption, or just copying what else has been done.

As this is a college design project they will be looking for you to apply your knowledge of the regulations and circuit design process.

As far as RCD protection goes you should go through all the situations which require RCD protection and decide which ones, if any, apply to your circuit.
For example a circuit serving a room containing a bath or shower requires 30mA RCD protection, so as part of the design process you ask the question 'does this circuit serve a room containing a bath or shower?'

You should write this all down as part of the design process so that the person assessing your work can see what you have done and crucially will be able to help if you make a mistake.

As for a TP+N MCB, it would be unusual to need one, for the vast majority of three phase circuits a TP MCB is adequate, and arguably preferable.

 

[Darkwood]

We need to be careful here, we don't do homework but we can nudge you slightly so ask members not to dish solutions out but no issue in seeing their calculations/solutions and nudging in the right direction - we don't learn by copy and paste!

 

[Robert2254]

Hi ,
Currently doing a design project in college and I need to pick a circuit breaker ( In device rating and type) for a food holding equipment unit that requires a 16A 400V three phase and neutral supply that is supplied by 5 core SWA. I think I should pick a 16A 3P+N RCBO but wasn't completely sure so thought I would run it by on here 1st before I write anything down.

you don't need an rcd unless you are supplying the equipment via a socket outlet of 32A or less. If you are wiring through a local isolator to fixed or immovable equipment you do not need an RCD. A 16A tp mcb will do just fine probably type C

 

[westward10]

you don't need an rcd unless you are supplying the equipment via a socket outlet of 32A or less. If you are wiring through a local isolator to fixed or immovable equipment you do not need an RCD. A 16A tp mcb will do just fine probably type C

Assuming ADS is provided without the provision of an RCD.

 

[Robert2254]

Assuming ADS is provided without the provision of an RCD.

Are you discounting the ADS in favour of the rcd? because that only applies on a TT supply

 

[westward10]

Are you discounting the ADS in favour of the rcd? because that only applies on a TT supply

Can you reinforce that statement.

 

[Robert2254]

well doesn't that circuit need to be protected like all the other circuits which are all rcbos so I thought it would be best for this to be a rcbo instead of a 3P+N MCB with a RCD. But am I right to use a 3P+N breaker for 3 phase though ?

only need an RCD device if you are supplying the equipment through a socket. Otherwise it's just a triple pole mcb and neutral isn't switched.

 

[wsoppitt]

So guys , for example supply to 3phase roller shutter door motor with attached 1m lead , if socket was high level ( say 3.5m up ) controlled by low level isolator, would you still put it through an rcd ?

 

[westward10]

So guys , for example supply to 3phase roller shutter door motor with attached 1m lead , if socket was high level ( say 3.5m up ) controlled by low level isolator, would you still put it through an rcd ?

Yes.

 

[davesparks]

only need an RCD device if you are supplying the equipment through a socket. Otherwise it's just a triple pole mcb and neutral isn't switched.

This is incorrect, there are many reasons why an RCD may be required.
There is not enough information in the OP to make this decision.

 

[davesparks]

So guys , for example supply to 3phase roller shutter door motor with attached 1m lead , if socket was high level ( say 3.5m up ) controlled by low level isolator, would you still put it through an rcd ?

There is no exception for height or accessibility in the regulations.

The designer of the installation may do a risk assessment to justify not providing RCD protection if there is some reason why RCD protection may be undesirable.

 

[Vortigern]

I think the above is a good nudge for you to consider carefully. Medical supplies kept in fridges at surgeries, would you RCD that circuit?

 

[davesparks]

I think the above is a good nudge for you to consider carefully. Medical supplies kept in fridges at surgeries, would you RCD that circuit?

Yes, but i'd put them on their own dedicated circuit.

 

[Flanders]

You will need to now if there is start up current on the equipment. To choose what type of mcb / rcbo B C or D .Also Just wondering if 16amp ocpd is a bit close to the limit if the equipment demand load is also 16amps.