Questions regarding testing for Main/Sub Distributor board.

[nazoom]

My test examination board is domestic (single phase) and has two Distributor boards (D/B), one the main one with the main switch feeding a sub D/B, and the other one is external (sub) distributor board with no main switch but they are RCD protected and is fed by the main D/B. My question is when recording and testing the main board for PFC and Ze do we use the same values (measured at Main) for the both main and sub main distributor board or do I have to test both distributors independently and then record the different results in a different Schedule of test results sheet?

Many Thanks

 

[GaryM]

I'm not sure I understand totally. Let's call them DB1 and DB2.
DB1 is your main DB. Is DB2 (sub board) fed from a circuit within DB1 (main)?

 

[nazoom]

Yes that's correct. The DB1 has main switch but DB2 (Sub) is fed form the DB1 and has a n RCD protecting two circuits. The DB2 has it own small neutral terminal and an earthing terminal but smaller than the one in the DB1.

So my question is do I need to carry out the tests for Ze and PFC one for each DB or do I just carry out the tests (Ze and PFC) for the main DB1? and record the same result in the Schedule for Ze and PFC for both DB?

Please help.

 

[tony mc]

You will only have 1 ZE that is your main DB .

The PFC will also be taken at the main board.

On DB 2 you will have a ZDB and if you were to do a PFC it will be lower due to the increase in resistance.

On your schedule of test resuls for DB1 you will have the R1 + R2 of the supply cable from DB 1 to DB2 !

 

[GaryM]

There's only one Ze and that's at the origin (incoming at DB1).
DB2 is essentially a final circuit from DB1 and will have the Zs reading taken at the incoming terminals at DB2 recorded on DB2's schedule of test results as Zdb. Pfc will also be taken at the incoming terminals of DB2.

 

[nazoom]

So for PFC at DB2, I use the three leads connecting at DB2 as follows:
Does the Red probe go on the Line on the RCD itself in the DB2,
Does the Black probe go on the Neutral terminal of DB2 or at the N hole on the RCD itself?
The yellow/ Green probe go on the MET at the DB2?

Thanks again.

 

[GaryM]

No, normal 2 probe PFC test.
At DB2, test between L-N (PSCC) and L-E (PEFC) with your two probes (red or brown and green) then record the highest value as PFC.
I'm assuming this is single phase though you mention DB and not CU. If it is 3 phase then also measure between phases if your meter is capable, if not then double the L-N PSCC value and record that if it's higher than the PEFC value.

 

[nazoom]

In the CU2 there is and RCD protecting the CU2 circuits. This RCD is fed form the main DB1. So for testing the PFC in the CU2 we test between L-N and L-E. But where does the probes go? do we connect the probes to the holes in the RCD (holes L and N) in the CU2? And then between the L-E in the Rcd (Line hole and MET for C/U2)? Then record the highest.

Please Help.

 

[GaryM]

Yes, where the incoming conductors terminate.

 

[nazoom]

Hi tony mc

You mentioned that I need to carry out the R1+R2 for the supply cable. How do we do that? Where do we make contact if the DB1 supplying the CU2. So where does the black and red probes make contact with? and in which Consumer unit do we make contact with the probes?

Please Help.

Thanks

 

[GaryM]

You'll do an R1+R2 test for all final circuits fed from DB1.
DB2 is one of those final circuits. Just treat it like any other final circuits.

 

[Guitarist]

nazoom. Do you know how to do an R1+R2 test? I think we need to establish the extent of your knowledge before proceeding.

 

[nazoom]

Of course I know how to do R1+R2 test! R1 requires a line connection and R2 an earth connection, where do i find these in the CU2 as it is been fed by the Main DB1? Am I right to assume that the point of contact between the line feeding the CU2 (R1)and the MET in the CU2 (R2)?

Thanks again.

 

[GaryM]

You're measuring the resistance of the line and cpc conductors that leave the MCB and earth terminal in DB1 and terminate to the incoming side of the main switch/rcd of DB2 and earth terminal.
Disconnect both the incoming line and cpc from DB2 and temporarily connect them together. Now measure the resistance between line and cpc that leave DB1.
It's pretty basic stuff. If you're in need of a refresher (don't be afraid to admit it, or take insult) then just have another browse through Guidance Notes 3.

 

[tony mc]

At DB1 you will join line and CPC of the DB 2 circuit (Isolated etc) then at DB 2 measure the resistance of the conductors which is your R1 + R2 ( make sure the main switch is off on DB 2 )

You will find these connected to the main switch of DB 2.

It matters not which end you link as the cable resistance will be the same.


It must be pre exam nerves !

i

 

[tony mc]

Must type faster :crazy:

 

[nazoom]

I just need to clarify this and make sure i got it right!

So what happens at DB2? Where do I make contact there for R1 +R2 value?

1-Do I use the RCD Line (L) hole, and the MET as my connections to measure R1+R2 at DB2? I mean link the Line and cpc at DB1 and then use one of the probe to make contact with line (L) hole for RCD in the DB2 to measure R1, and at same time make contact with other probe to MET and this will measure R2?

OR

2- I Link the Line and cpc at DB1, and then disconnect the feed Line in the DB2 (conductor coming from the DB1 to DB2) this is R1 and make contact with one probe, then disconnect the CPC at DB2 (coming from the DB1 to DB2) and use the other probe to make contact here. Will this give the R1+R2 value for the supply cable?

 

[GaryM]

Have you ever done an R1+R2 test before? Do you understand the principle and reason why a R1+R2 test is carried out?
Above, both Tony and I have explained how to do it, being one of the more basic tests and you still don't seem to grasp it.
Do you have a copy of Guidance Notes 3?

 

[Guitarist]

Of course I know how to do R1+R2 test! R1 requires a line connection and R2 an earth connection, where do i find these in the CU2 as it is been fed by the Main DB1? Am I right to assume that the point of contact between the line feeding the CU2 (R1)and the MET in the CU2 (R2)?

Thanks again.

I'll shut up then...

 

[nazoom]

Thanks Tony.
So in DB2 there is an RCD but no mains switch, do i treat this RCd as the main switch or do I just disconnect the conductors feeding this RCD ( which are the Line and Earth coming from DB1) and carry out R1+R2 on these conductors?

Many thanks.

 

[nazoom]

Thanks Tony.

So in DB2 there is an RCD but no mains switch, do i treat this RCd as the main switch or do I just disconnect the conductors feeding this RCD ( line) and Earth coming from DB1 and carry out R1+R2 on these disconnected conductors? Also linking in the DB1.

Many thanks


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[needasparks]

Only just seen this thread and can't really add to what the others have said as it is such a basic test but reading your OP again I'm not sure whether the confussing part is your supply to DB2. Is this from an MCB way of DB1 or from the same origin of DB1 ? as you say from the main switch. Does this mean you have doubles tails in the main swtch ?
A picture can help alot with these basic questions so people can get their heads round it and advise.

 

[GaryM]

He said that CU2 is a final circuit fed from an MCB in DB1.
i've explained as much as I can and asked questions which he's failed to answer so I'm not sure how I can help anymore.

 

[nazoom]

The Sub fuse is the first circuits in the DB1. There is a conductor connecting from this first sub fuse in DB1 to feed the DB2. This Conductor (Line) terminate in the RCD (Which is the first thing in DB2. Then this DB2 has two circuits protected by this RCD. In DB2 there is also Small MET and small Neutral terminal.
The confusion part is where do the probes go when measuring continuity (R1+R2) for the sub fuse feeding the DB2? I know I have to link this Line and cpc in DB1, but then where do the probes go in DB2 to measure R1+R2 for this sub fuse?

 

[GaryM]

Look above, both Tony and I have explained how to carry out a R1+R2 test in this case, which is no different to any other radial circuit.

 

[Des 56]

I know I have to link this Line and cpc in DB1, but then where do the probes go in DB2 to measure R1+R2 for this sub fuse?​

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I am going to have a crack :ihih:

Wherever the ends (live and earth)are connected in DB2, that is where you get R1+R2
Shove a crocodile clip on the earth bar and your probe wherever the live is terminated

 

[nazoom]

Thanks Des 56. That's all I wanted to know is where the probes connect to in the DB2 to measure R1+R2.

Thanks to all.

 

[RogertheBodger]

Well done Des! must be the way you tell em.

 

[Des 56]

Well done Des! must be the way you tell em.

I think its like that old saying,"the blind leading" and all that :blush5:

 

[Guitarist]

I really can't believe how convoluted a simple R1+R2 test became.
It would have been quicker to get an electrician involved though