Unusual RCCB connection

Abhi

Member
Location
Jharkhand, India
I have a 4 pole 415 volt RCCB and a 2 phase 415 volt welding machine. How to connect this welding machine with 4 pole RCCB so that my purpose of electrical safety is achieved and,RCCB also work at its full potential?
 

mbrooke

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Do you have a picture of the RCCB?

Connect as you would with a 4 wire application, but simply do not involve the pole not hooked up to the circuitry/test resistor. Run the neutral to the RCCB source side, but don't use it on the load side.
 

Abhi

Member
Location
Jharkhand, India
Do you have a picture of the RCCB?

Connect as you would with a 4 wire application, but simply do not involve the pole not hooked up to the circuitry/test resistor. Run the neutral to the RCCB source side, but don't use it on the load side.
I have posted image of RCCB
 

mbrooke

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I think it will work as a mcb and not as a rccb. For behaving it as rccb, neutral must be involved
I do not think your RCCB pictured has short circuit and overload protection. Just differential protection.

Yes- in order for the test resistor to work neutral must be provided and involved with the RCCB.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
I think it will work as a mcb and not as a rccb. For behaving it as rccb, neutral must be involved
It is in both of mbrooke’s diagrams in that the neutral is being sensed by the summation CT. Whether or not your load actually connects to that neutral is irrelevant to the operation of the RCCB. Current out to the load on either pole must equal current returning on the other. No neutral current flowing just means that the neutral current, or rather lack of it, is irrelevant to the residual equation.
 

Abhi

Member
Location
Jharkhand, India
It is in both of mbrooke’s diagrams in that the neutral is being sensed by the summation CT. Whether or not your load actually connects to that neutral is irrelevant to the operation of the RCCB. Current out to the load on either pole must equal current returning on the other. No neutral current flowing just means that the neutral current, or rather lack of it, is irrelevant to the residual equation.
Yes, my load is a double phase welding machine which requires only two phase wire of 415 VAC 3 phase. There is no provision for neutral connection.

If I connect only two phase load to any two of the three poles of RCCB then it must work, as you told.

And plz explain about testing part of 4 pole RCCB
 

Abhi

Member
Location
Jharkhand, India
I did not connected any load to RCCB and supplied only 3 phase. And neutral was also not connected. I don't understand, how test circuit worked. Plz help

I have attached some pics for reference


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Abhi

Member
Location
Jharkhand, India
Your RCCB will function as a summation of all the current passing thru it-->all should sum up vectorially to zero. Any current that will not be sensed by the breaker will be treated as "leakage" and it's up to the breakers sensitivity to either trip or not(I sensitivity >30ma)! Not wiring the neutral (if load does not need a neutral) means there will be no current thru it even if you wired it in. Test button simply simulates a leak on the trip circuitry of your breaker by allowing a small amount of current to pass outside of you CB's summation CTS, a resistor of a value just enough to imitate a leakage current above the sensitivity setting of the RCCB. See it here:
But the test circuit is between pole 5 and neutral only, that means a valid complete circuit happens only pole 5 and neutral and not with any other poles. Then, how test circuit gets closed when only connecting 3 phases.

I have used multimeter to check in which poles the test circuit exists and i found the same as I said above.

I think you got my point.

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Last edited:

Abhi

Member
Location
Jharkhand, India
I apologise to all members bcoz during operation of test circuit, the neutral wire was connected and I did not noticed it. Sorry for wasting your valuable time.

The concept of RCCB is now clear to me
Thanks
 
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