And I'm struggling to understand how one could have that, how one could have current flowing in only one of the line conductors, unless it were flowing to earth.
Upgrade to 3 phase
- Thread starter SUNRAY
- Start date
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Two different kinds of balanced are being confused.
OK like so many of these threads I think we are at crossed purposes.
Hopefully this will clear the confusion:
No.1 is a multicore cable with a neutral. The CABLE and the RCD will be balanced regardless of the balance of the PHASES
No.2 is a multicore cable without a neutral. The CABLE and the RCD will be balanced regardless of the balance of the PHASES
No.3 is a multicore cable with a neutral. The CABLE will be balanced regardless of the balance of the PHASES, but the RCD will trip if there is any sort of imbalance of the PHASES .
So far the magnetic fields around the CABLE are minimal.
No.4 where the neutral is run separately for some reason, or the whole thing is in singles [very typical with temp genny feeds], the RCD is balanced and happy but the magnetic fields are potentially a problem.
Hopefully we are now on the same song sheet.
Indeed, I'm hoping that post #63 [which I started 3 hours ago] has clarified the confusion.
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It does.Agreed.
I don't really get that one. Unless the currents in the three phases are identical, there will surely be a finite vector sum of the currents, won't there (i.e. the cable is 'not balanced'). Think of fairly extreme situations, in which there iis little or no current in one or two of the phases. In such a situation, if only the three phases ( but not neutral) went through the RCD (per your diagram), the RCD would trip, wouldn't it?
In any event, an RCD which had only phase conductors going through it would surely serve no useful purpose - since it would not detect phase-neutral imbalanceds due to faults to earth?
Kind Regards, John
Doesn't the magnitude of the vector sum of the currents in the 3 phases always equal zero in this case?
Edit - 'cos, referring to EFLI's post below - if there is no neutral then there is nowhere for any unbalanced current to flow. You can't connect a load between phase and neutral if there is no neutral, so all loads must be phase-phase.
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Re: #2
The test button on three phase RCDs does not use the neutral.
If there is a neutral not running through the RCD, it would, but not if there is no neutral.
Surely it will still detect residual current.
The test button on three phase RCDs does not use the neutral.
I was not talking about a situation in which there "is no neutral" (at all) - but, per what SUNRAY appears to have been talking about, a situation in which there is not a neutral in the same multicore cable as the 3 phase conductors (i.e. as per case 4 in his post #63).
Kind Regards, John
I was using this for information:
On further investigation, I find some which do (or show they do) connect the test button circuit to the neutral, so ...
On further investigation, I find some which do (or show they do) connect the test button circuit to the neutral, so ...
Indeed, but we seem to have 'cross-purposes' again, since I've been talking about a situation in which there was a neutral, but not in the same cable as the phase conductors.
Again, seemingly cross-purposes. If the circuit has a neutral, it must pass through the RCD. Apart from anything else, if it didn't, the RCD would trip unless there were perfect phase balance.
Dunno. I've never used them, let alone taken one apart (I use separate L+N RCDs for each phase in my house). What does the test button do, then?
Kind Regards, John
If you have no neutral, and no current in two phases, where is the circuit which you need for there to be current in the third phase?
But you were not talking about that situation in your reply to Sunray.
Look at the drawing, and compare it to #3 & #4.
#2 is not "a situation in which there was a neutral, but not in the same cable as the phase conductors", that's #s 3 & 4.
#2 is the situation where there is no neutral anywhere.
Look at the drawing, and compare it to #3 & #4.
#2 is not "a situation in which there was a neutral, but not in the same cable as the phase conductors", that's #s 3 & 4.
#2 is the situation where there is no neutral anywhere.
hahaha, once again none of them know what the other is talking about, the waffle has got too deep.
And drawing no3 is nonsense, because it is a ficticious circuit that would never be used, any sp load will trip the rcd
EDit - Didn't realise the drawing was ficticious
And drawing no3 is nonsense, because it is a ficticious circuit that would never be used, any sp load will trip the rcd
EDit - Didn't realise the drawing was ficticious
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