Washing machine and new consumer unit

[Risteard]

Hi John,

Believe it or not Housing Executive properties here tend towards RCBOs for each circuit.

Regards,
Risteard

It's very common in the social housing stock here to have dedicated circuits for the likes of washing machines.

When you say "dedicated circuit", do you mean with its own dedicated RCD or RCBO (since that is what would be relevant in terms of the way this issue arose in discussion)?

Kind Regards, John

 

[Adam_151]

Hi John,

Believe it or not Housing Executive properties here tend towards RCBOs for each circuit.

When you consider that individual RCBOs for each circuit should

A) greatly reduce the likelyhood of a nuisence trip
B) In most cases in the event of a actually fault reduce the inconvience suffered to that which can be tolerated until the next working day

It probably works out cost effective overall... the install cost is higher, but that is outweighed by a lot less out of hours call out fees

I know hager did market a single pole and switched neutral (SPSN) MCB based split load consumer unit for housing associations, so that if the RCD tripped and could not result, a help desk opperator could, following a script, get them to isolate all circuits and switch on one at a time, therefore avoiding sending someone out till the morning in the vast number of cases. I do not believe there was much take up of it though

 

[EFLImpudence]

As you know the writers of BS7671 are very aware of English used,

That is frequently doubtful.

swapping phrases like rule of thumb to historical.

So, changing the meaning.

So if they mean over non leakage current or over leakage current I am sure they would stipulate, likely in the definitions section.

See Definitions Part 2 of overcurrent.

Also, would the fact that leakage is not mentioned at all be a clue?

Most British Lawyers are very good at reading English. If it were a statement by a layman I would accept that they mean current protected by the MCB not RCD,

See Definitions.

just like a statement using a double negative is likely an error.

No, it isn't but previous posts indicate that you are confused as to what is a double negative.

But BS7671 is hardly a layman's book.

They would seem to think it is hardly an electricians' book either judging by the huge number of guides explaining it.

 

[JohnW2]

The ELCB-v that I met was a 200 ohm coil that operates the trip when 20 mA flowed through the coil. For 20 mA to flow the voltage across the coil had to be 40 volts.unlike the ELCB-v which measured voltage

Indeed, and we've discussed this before. They were essentially (low-current) current-operated solenoids, operated by the current flowing through them. One could, of course, multiply the trip current by the coil resistance to get the 'operating voltage', but that's a bit artificial - the 'voltage being sensed' would be zero were it not for the presence of the VOELCB! It's just like relays etc. - the spec is usually quoted in terms of 'operating voltage', but it's actually the resultant current that causes the relay to operate.

I believe that genuinely voltage operated devices were available with coils of much higher resistance ( impedance ) and these tripped on less than 1 mA but these often tripped during thunderstorms when the potential of the ground was bounced by a lightning strike somewhere near by.

That would have presumably required a separate, 'remote' earth rod - if one inserted a high resistance in the connection between the installation and its primary earth electrode, it would be questionable as to whether that earth electrode was serving any useful purpose, other than facilitating the operation of the VOELCB!

Kind Regards, John

 

[JohnW2]

Hi John, Believe it or not Housing Executive properties here tend towards RCBOs for each circuit.

Interesting. As Adam has said, in that situation it might be cost-effective.

Kind Regards, John

 

[JohnW2]

As you know the writers of BS7671 are very aware of English used ... So if they mean over non leakage current or over leakage current I am sure they would stipulate, likely in the definitions section.

They more-or-less do. The definition of "overcurrent" in Part 2 is:[quote="part 2 of BS7671]"Overcurrent. A current exceeding the rated value. For conductors, the rated value is the current-carrying capacity"[/quote]I doubt that you'll find any cables in use by electricians which have a CCC of 30mA!

As I've said, we all know (and I'd be very surprised if a Court did not agree!) what 'overcurrent protective device' means in the context of the BS7671 definition of 'a circuit' - so I really don't understand why you are muddying the waters.

Kind Regards, John

 

[EFLImpudence]

Could it be said that the RCD is NOT an over-current device because a current of over 30mA is NOT detected?

It is just seen by the RCD to be missing - under-current, in fact, in the neutral.

 

[JohnW2]

Could it be said that the RCD is NOT an over-current device because a current of over 30mA is NOT detected? It is just seen by the RCD to be missing - under-current, in fact, in the neutral.

All sorts of things 'could be said'! However, I think that (virtually!) all of us know what 'overcurrent', 'overcurrent protective device' and 'RCD' are, so any debates are both moot (for virtually all of us) and, I would say, rather 'silly'!

Kind Regards, John