reusing a disused shower circuit

[ban-all-sheds]

I fundamentally disagree. It's about an existing cable, not an existing circuit, and it's all about designing.

The rated current or current setting of the protective device (In) must not be less than the design current (Ib) of the circuit, and the rated current or current setting of the protective device (In) must not exceed the lowest of the current carrying capacities Iz) of any of the conductors of the circuit.

Ib = 6.5A
In = 30A
Iz = 47A (accepting flameport's reasoning).

So why must In be reduced, Goldberg?

 

[Goldberg]

I dont understand

Imagine a radial circuit with a design load of 5A - let's make it easy and say the conditions make it acceptable to use a type B 6A MCB and 1.0mm² cable.

If I then chose to 6mm² cable, for my own secret personal private secret private reason, would you then change the CPD to a 40A MCB?

If not, then why not, SUNRAY?

 

[ban-all-sheds]

That is not the same - please stop evading the question by trying to make it look as if a different one is being asked.

We have a circuit where the following applies:

Ib ≤ 30A
In = 30A
Iz = 47A

i.e. Ib ≤ In ≤ Iz

We are going to change Ib to 6.5A.

i.e. Ib ≤ In ≤ Iz

YOU were the one who said that In needs to be changed to a different number between 6.5 and 47.

So please stop responding by asking a question of your own, and answer this one:

Why must In be changed?

 

[Goldberg]

Mon Aug 17, 2009 12:41 am

If not, then why not?

Mon Aug 17, 2009 7:58 am

So why must In be reduced?

If your question is not the same, then please start a new topic and ask it there.

 

[ban-all-sheds]

Stop repeating your question to Sunray - it has nothing to do with my question to you concerning the assertion which you made before that.

Why must In be reduced?

But if you insist in believing that you can successfully answer that question by ignoring it, let's try this one:

I was asking why is is neccessary to change the CPD when whats there is OK, you dont need to downrate just because its being used below capacity.

What's there isn't OK.

Why isn't 6.5 ≤ 30 ≤ 47 OK?

 

[Goldberg]

Stop repeating your question to Sunray - it has nothing to do with my question to you concerning the assertion which you made before that.

You're so quaint with your idea that you can command other members to do what you want.

If you want to question kai's assertion that the 'MCB' be changed, then go right ahead - nobody is stopping you. I expect that kai will ignore you though, in the same way that SUNRAY has ignored me.

Perhaps SUNRAY just thinks that I'm a tw@, or a w*nker. Perhaps you do too, and just aren't honest enough to say so. Who knows?

 

[ban-all-sheds]

Stop repeating your question to Sunray - it has nothing to do with my question to you concerning the assertion which you made before that.

You're so quaint with your idea that you can command other members to do what you want.

I do apologise for not using the word please often enough.

I asked you a civil and relevant question, which you responded to by repeating a question you had asked someone else.

I don't think it is "quaint" to expect a proper answer, I think it's perfectly reasonable.

Will you please stop repeating your question to Sunray - it has nothing to do with my question to you.

Will you please do me the courtesy of directly answering my question.

If you want to question kai's assertion that the 'MCB' be changed, then go right ahead - nobody is stopping you. I expect that kai will ignore you though, in the same way that SUNRAY has ignored me.

Kai's assertion?

I was asking why is is neccessary to change the CPD when whats there is OK, you dont need to downrate just because its being used below capacity.

What's there isn't OK.

Why isn't 6.5 ≤ 30 ≤ 47 OK?

Perhaps SUNRAY just thinks that I'm a tw@, or a w*nker. Perhaps you do too, and just aren't honest enough to say so. Who knows?

How much longer are you going to carry on behaving like this?

 

[SUNRAY]

Taylortwocities, thanks for the correction, I didn't realise the initial omission and read it the way you meant it to be.

Goldberg, I have not been replying as I don't want to feel responsible for this going in a completely wrong direction.
I am glad that BAS calculations are saying the same as mine, I was starting to question my understandings.
Goldberg you have asked me this question:-
"Imagine a radial circuit with a design load of 5A - let's make it easy and say the conditions make it acceptable to use a type B 6A MCB and 1.0mm² cable.
If I then chose to 6mm² cable, for my own secret personal private secret private reason, would you then change the CPD to a 40A MCB?
If not, then why not?
After all, the 40A MCB would protect the cable."
I believed I answered by making a direct comparison between the original question (6mm/30A fuse) and the standard ring main.
Perhaps it is rude of me to not answer again as you have asked it several more times since, so here goes.
When you supply the rest of the information thats required when designing circuits, so I have all the facts I need, I will give an opinion on the requirements.
If you don't know what is required then I suggest you start a new thread "What information do I need when designing a circuit". I'm sure there are plenty of people on here who will be only too pleased to assist you.

 

[londonboy]

goldberg why dont you just stop now.
now that you know your wrong.

 

[Goldberg]

Will you please do me the courtesy of directly answering my question.

All in good time.

Goldberg you have asked me this question:-
"Imagine a radial circuit with a design load of 5A - let's make it easy and say the conditions make it acceptable to use a type B 6A MCB and 1.0mm² cable.
If I then chose to 6mm² cable, for my own secret personal private secret private reason, would you then change the CPD to a 40A MCB?
If not, then why not?
After all, the 40A MCB would protect the cable."
I believed I answered by making a direct comparison between the original question (6mm/30A fuse) and the standard ring main.
Perhaps it is rude of me to not answer again as you have asked it several more times since, so here goes.

I didn't find it all rude, and I applaud your desire to avoid a deviation from the original point.

When you supply the rest of the information thats required when designing circuits, so I have all the facts I need, I will give an opinion on the requirements.

You gave your opinion on the design of jpbunce's circuit, and you didn't have the facts before doing that, so I don't understand your reticence with choosing the correct CPD for a hypothetical radial where the design load is 5A (resistive) and the cable is 6mm² with no de-rating factors applying.

 

[ColJack]

if the load is directly connected then as close to the 5A as you can get..
however if, as in the example, several pieces of equipment will be connected to it and fused down at the point of connection, then I see no problem with having a larger CPD on the circuit as long as it is suitable for the cable..

 

[SUNRAY]

Will you please do me the courtesy of directly answering my question.

All in good time.

Goldberg you have asked me this question:-
"Imagine a radial circuit with a design load of 5A - let's make it easy and say the conditions make it acceptable to use a type B 6A MCB and 1.0mm² cable.
If I then chose to 6mm² cable, for my own secret personal private secret private reason, would you then change the CPD to a 40A MCB?
If not, then why not?
After all, the 40A MCB would protect the cable."
I believed I answered by making a direct comparison between the original question (6mm/30A fuse) and the standard ring main.
Perhaps it is rude of me to not answer again as you have asked it several more times since, so here goes.

I didn't find it all rude, and I applaud your desire to avoid a deviation from the original point.

When you supply the rest of the information thats required when designing circuits, so I have all the facts I need, I will give an opinion on the requirements.

You gave your opinion on the design of jpbunce's circuit, and you didn't have the facts before doing that, so I don't understand your reticence with choosing the correct CPD for a hypothetical radial where the design load is 5A (resistive) and the cable is 6mm² with no de-rating factors applying.

Goldberg
I am very sorry for you that you are unable to supply ALL the information required to design your hypothetical circuit. The remaining information is still missing.
I am just as sorry that you are unable to see that all the information is present to establish the requirements for the real circuit (save the derating, which had already been discussed!).

I suggest again that you start that new thread.

I feel this conversation has now found an appropriate position to draw to an end.

 

[Goldberg]

I am very sorry for you that you are unable to supply ALL the information required to design your hypothetical circuit.

No need to be sorry for me - the sad thing is that this has exposed your reluctance, or perhaps your inability, to reason and infer. Let's not forget that it was you who wrote that you didn't understand.

 

[ban-all-sheds]

I was asking why is is neccessary to change the CPD when whats there is OK, you dont need to downrate just because its being used below capacity.

What's there isn't OK.

Why isn't 6.5 ≤ 30 ≤ 47 OK?

 

[ColJack]

Let's not forget that it was you who wrote that you didn't understand.

now lets be fair here, you deliberately misquoted him..

I dont understand the 'problem' here surely the cable must be protected by the 'fuse', at the end of the cable a couple of FCU with fuses rated at 5A & 3A would be spot on, as long as the RCD is there somewhere and the cable will fit into terminals of of the FCU's.
Am I missing something?

is what he actually said..
he was voicing objection to the error that was posted saying that the CPD needed changing when clearly it doesn't..

what the OP has is a 30A radial with 2 points of utilisation on it..
the points of utilisation are fused down by the use of FCU's.. so no differerence to a 30A radial for use with sockets..