Contactum RCBO- am I doing something wrong

[ac1951]

Hi all,

I just fitted a Contactum 20A RCBO into a Contactum 17th edition CU. I installed it on one of the non RCD protected ways.

I have connected the blue wire from the RCBO to the incoming Nuetral bar and this is also the point where the CCT (being supplied by the new RCBO) Neutral is connected.

However, as soon as anything is connected to the cct the RCBO trips. I have moved the cct onto a spare 16A MCB protected by one of the CU's

30mA RCDs and have no problems !!

Am I missing something or is the RCBO duff ........

thanks Andy

[Toby]

The neutral of the circuit should be connected to the neutral output of the RCBO, NOT the consumer neutral rail directly.

If it is one of these

if you look at the top of the unit, it appears there is a N Out terminal on the top somewhere!

Toby...

[stan]

Assuming RCBO are similar to what here in North America we call (incorrectly IMO) a GFI they operate to protect the circuit so equipped when the current through the live and neutral leads differs. So both the live and neutral leads need to go 'through' the RCD? Other wise the RCD will operate every time current flows through the one connected (live) lead?

[ARWadsworth]

Assuming RCBO are similar to what here in North America we call (incorrectly IMO) a GFI they operate to protect the circuit so equipped when the current through the live and neutral leads differs. So both the live and neutral leads need to go 'through' the RCD? Other wise the RCD will operate every time current flows through the one connected (live) lead?

Correct. Andy just had either a blonde/grey moment.

Easliy done.

Adam

[Andy Wade]

To clarify, an RCBO (Residual current Circuit Breaker with Overload) is the combination of a residual current circuit breaker (RCCB, equivalent to the North American GFCI) and an MCB. It provides both residual current *and* overcurrent protection.

When we talk about RCDs on this side of the pond we usually mean RCCBs, i.e. devices providing only residual current protection and not overcurrent protection. This is lax use of terminology really, because 'RCD' is a generic term embracing (/inter alia/) both RCCBs and RCBOs.

Indeed, but you introduce more terminological inexactitude. Formally we speak of the _Line_ and Neutral conductors, both of which are live (i.e. current carrying). Use of 'live' to mean 'line' is common parlance though strictly incorrect. Which interpretation of live is meant is usually clear from the context though, once you're aware of the scope for confusion.

[John Rumm]

This sounds like the area where you probably have the problem.

Both the line and neutral from the circuit need to connect to the RCBO - note the neutral does not connect to the busbar in the CU. The neutral wire from the RCBO must in turn connect to the busbar.

If the RCBO powers up without tripping when no circuit wires are are connected, and then trips when its test button is pushed, then its probably ok.

[John Rumm]

these

>>> Then if you look at the top of the unit, it appears there is a N Out

Yup. Have a look at the last picture ("DIN rail mounting RCBO") in this section - that is what is being discussed here:

[ac1951]

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Toby, John, thanks for the fedback..

DOH ..... I should have known that but after fitting the RCBO the Neutral cct connection is hidden at the back of the unit and I then proceeded to connect the cct Neutral to the Busbar whilst all the time thinking this doesn't seem right ..

Andy