site temp

[rich67577]

Hi guys need some help I've got a 3 phase supply to connect to a 3 phase site transformer via a 3. Phase rcd unit mounted on the transformer on the out going supply to the transformer from the rcd unit were do I connect the natural as the transformer has no neutral just 3 phase and earth but with no neutral the transformer will not trip the rcd

 

[Plonker 3]

Do you know how to read a instruction manual?

 

[Guest111]

If the transformer just has 3 phase input without a neutral then there is no need for a neutral so that's why there is no place to connect one,not needing a neutral is pretty common on lot's of 3 phase stuff.

 

[rich67577]

Ok I might of worded this wrong the rcd unit feeds the transformer I no the transformer has no neutral at it what I can't work out is how's the rcd ever going to trip if a faulty lead or machine is pluged in to the transformer if it has no natural going throw the load side of the rcd to the transformer

 

[Guest111]

Ok I might of worded this wrong the rcd unit feeds the transformer I no the transformer has no neutral at it what I can't work out is how's the rcd ever going to trip if a faulty lead or machine is pluged in to the transformer if it has no natural going throw the load side of the rcd to the transformer

If something faulty is plugged into the transformer it wont trip an RCD on the transformer feed side anyway,the whole point of the transformer is to provide isolation.

 

[rich67577]

Problem is the designer had spec an transformer with rcd

 

[Guest111]

The RCD on the transformer feed side is a pointless excercise if he thinks that it's going to protect the load side.Best you explain to him how a safety isolating transformer works,either that or get an rcd that will work on the load side.

 

[trev]

if it has no natural going throw the load side of the rcd to the transformer

You use that term a lot, can you explain what one is because I've not come across the term so either I've got gaps in my knowledge or you should be passing this job on to someone with experience of 3 ph systems

 

[rich67577]

I've got plenty experience in three phase just never been asked to fit an rcd to a site temp before I no it has no neutral at the transformer so was trying to work out how the rcd would work with out one

 

[Richard Burns]

If you have a current leak to earth then the current will not be going back to the RCD so it will sense an imbalance and trip.
The test function may need a line connection to the neutral terminal of the RCD, assuming it can be set up that way.

 

[Darkwood]

Your thinking about it the wrong way - an rcd monitors an imbalance of current flowing into and out of the circuit, not all circuits have a N some circuits work across the PD of the different phases and any leak from a phase to earth will create an imbalance where if large enough it will trip the rcd. Neutral is a Live wire in disguise as its just at the same potential as earth if you think about it.

 

[Guest111]

Your thinking about it the wrong way - an rcd monitors an imbalance of current flowing into and out of the circuit, not all circuits have a N some circuits work across the PD of the different phases and any leak from a phase to earth will create an imbalance where if large enough it will trip the rcd. Neutral is a Live wire in disguise as its just at the same potential as earth if you think about it.

well put,which is exactly why certain test lamps trip an RCD when you test phase to earth.