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1Justin

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I have a big place to work on here. Have come across a long lighting circuit where I need to repair/extend damaged end of the circuit. There are 8 PL type Florescent loads distributed evenly.

Due to the (measured & validated) R1+R2, since the circuit is probably ~>60M long in 1.5 T&E, I need to downgrade the ex. MEM C type 10A to a 6A, - and maybe go B type for extra margin. (And TBD fit a MEM RCD pod along with it).

Q) Would B type breaker in your learned opinions be a mistake with 8 off PL type 18W florescent loads (Is it likely to drop out on surge?)
 
About 2.5 and that's still ~ 13M from the farthest end. (on 10A c type). 6A C type could be borderline
 
How much does it cost for a 6amp B type. Get hold of one and give it a go....not much load, there.
 
I think that's pretty much my opinion. I like to be a little more predictive but not always easy. Maybe this will calibrate the yardstick so to speak.
RGds
 
4A C type might work?
 
6A type C would require a max. Zs of 3.8 ohms. that should comply.
 
and what reason do you have for fitting a RCD?
 
and what reason do you have for fitting a RCD?

Have to repair the end of the circuit where the gardener pulled down the ivy over the lamp, then cut off the cable flush with the wall! New cable from inside via different route. ..Whether that classifies as hidden cable in wall I'm still cogitating on. The current one is certainly hidden, I haven't found it yet.. the wall is about 600mm thick and cable vanishes outside not to appear under the floorboards :).
 
Contact the tech' of the mcb and ask for a chart regarding inductive lamps of different natures and how many are acceptable on a given mcb, its more to do with the issue of combined inrush if all the fitting switch on together as addition to that fact its good for the load and the Zs.
 
I wouldn't have thought twice about putting eight baby fluos on a B6. IIRC in our previous warehouse we had 24 x 36W on each B10 all switched together.
 
Put another way, you'd have to have some seriously inrushy ballasts to trip it. I'm not saying there aren't fittings out there that might cause hassle but they aren't in the same league as LED drivers. Watch the VD though...
 
Why are you worrying about the maximum Zs of the mcb in relation to its disconnection time if you have a 30ma rcd fitted ??
Your line to neutral loop impedance will probably comply because its gonna be lower than line to earth anyway. ie 1.5 + 1.0 vs 1.5 + 1.5.
 
I wouldn't have thought twice about putting eight baby fluos on a B6. IIRC in our previous warehouse we had 24 x 36W on each B10 all switched together.
I missed the wattage bit so they could have been modular 4x55w PL fittings which is a different ball game when switch multiples together... note to self-read the fricken OP fully!
 
Because it is very bad practice to rely on an unreliable device (RCD) for fault protection

Where does it say its bad practice, or is that just an opinion ??

So max Zs permitted by BS7671 where a 30ma rcd is fitted should never be 1667 ??
This is earth fault not line to neutral, and what makes an mcb any more reliable than an rcd ??

Sorry Dave, you know where I'm coming from with this mate.

411.5 Note 2 (and reg 542.2.2)
 
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I think he meant a circuit should where possible ie - tns/tncs - should be designed so zs complies in the first place and you shouldn't be in the mind of wiring and finding its too high then falling back on other regulations to cover your arse when that reg' was not designed to be used this way.
 
Where does it say its bad practice, or is that just an opinion ??

So max Zs permitted by BS7671 where a 30ma rcd is fitted should never be 1667 ??
This is earth fault not line to neutral, and what makes an mcb any more reliable than an rcd ??

Sorry Dave, you know where I'm coming from with this mate.

411.5 Note 2 (and reg 542.2.2)

I don't know where you are coming from at all!

RCDs regular fail periodic testing and suffer from issues if not regularly tested by pushing the test button.
Various studies have been carried out and RCD devices just don't continue to give reliable operation unless they are operated every 3 months by the test buttons.

MCBs and fuses are far better proven technology and don't need to be operated every 3 months to remain reliable.
 

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