Testing an additional ccu

[Eric M]

I have a homework question which I hope you will help me with. Heres the scenario.

I am called to inspect a 2 way CCU (in a garage for example) connected via SWA to the main CCU in the house. I notice there are banjo type connectors where the SWA joins the CCUs however there are no earth screws.

I install earth screws and fit fly leads to the earth bars at each CCU.

Question:
what is the correct procedure to test continuity of cpc at the 2 way CCU in the garage? I believe you could use r1+r2 for circuits fed from the secondary CCU but I assume you would also need to check the resistance between MET and secondary CCU earth bar ? Would it be a long lead method from MET to earth bar at secondary ccu? or am I missing something

Hope that makes sense.

 

[Guest55]

Carry out r1+r2 test with the submains just as you would with a final circuit , no different.

 

[Silly Sausage]

I'd carry out a Ze (Zdb in this case) test, in the normal way, on the garage CU, which would prove continuity, or not.

The SWA feed to it, I classify as a cct belonging to the main CU, which would be tested when that CU is tested.

 

[SirKit Breaker]

I'd carry out a Ze (Zdb in this case) test, in the normal way, on the garage CU, which would prove continuity, or not.

The SWA feed to it, I classify as a cct belonging to the main CU, which would be tested when that CU is tested.

I'm with Archy here, and the SWA is a "distribution circuit" not a final circuit, from the main CCU to your garage CCU, so depending on the protective device for that cable, you may have a different disconnection time. If it is protected by a 60898 mcb, then it is still 0.4 disconnection time, but if it is a fuse, it could be 5 seconds.

Cheers.............Howard

 

[Guitarist]

I'm assuming that they are referring to testing the cpc up to the CU in the garage.
I would isolate garage supply in the main CU, link Line and cpc in the garage, then test R1+R2 for that cable at the main CU. You can add this to your Ze to give your Zdb at the garage CU.
Of course, it could be done the other way round.

 

[Silly Sausage]

The more you read the question, the more ambiguous it gets. They don't make it easy sometimes, but it makes you think.
Trouble is they may give marks for one answer and not the other, quite valid, one.

 

[JUD]

I'm with Archy here, and the SWA is a "distribution circuit" not a final circuit... If it is protected by a 60898 mcb, then it is still 0.4 disconnection time, but if it is a fuse, it could be 5 seconds.

Can I ask you where it says this Howard.

I've always been led to believe that final circuits >32A and distribution circuits are 5 seconds (as per 411.3.2) regardless of the protective device.

 

[Eric M]

I'm assuming that they are referring to testing the cpc up to the CU in the garage.
I would isolate garage supply in the main CU, link Line and cpc in the garage, then test R1+R2 for that cable at the main CU. You can add this to your Ze to give your Zdb at the garage CU.
Of course, it could be done the other way round.

Thanks for the replies, I think this is the answer I'm looking for. Unless anyone else has any different ideas?