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VOLTAGE OPERATED ELCB BE842
StuartBa
7 Posts
Question
Regarding voltage ELCB's BS842 I am currently looking at replacing an old Wylex fuse board with a new C.U with individual rcbo's system is TT. Question is if I remove the earth connections from this device can it be used as the isolator switch for the new CU?
 
18 Replies
mapj1
2170 Posts
It will work as a rather lumpy isolator, yes, it just happens to have a pair of contacts that allow you to turn it off by remote control from a 50V supply! (a switch with an auxiliary coil we'd normally call that and pay accordingly) .
However, if there is any question about it's condition then the replacement should be a proper isolator or 100mA time delay RCD in the smallest possible plastic box would be a better choice. Are you adding surge protection ?
StuartBa
7 Posts
Thanks for your comments I've not thought of adding surge protection as its a small domestic building.
AJJewsbury
1677 Posts
I've not thought of adding surge protection as its a small domestic building.
Unless it really is tiny (e.g. domestic outbuilding - where replacing the entire installation and appliances would cost less than 5x the cost of fitting the SPD) you really should be doing the risk assessment at least.
  - Andy.
Sparkingchip
2675 Posts
There has been a jump from what to do about the main switch to should a SPD be installed, as this is a TT installation installing a combined main switch and SPD together in a metal enclosure is very problematic, so not something I would consider.

What layout of consumer unit are you installing, all 30 mA RCBOs with a main switch, dual 30 mA RCDs with a main switch or a single upfront 30 mA RCD as the main switch?

Andy b.
AJJewsbury
1677 Posts
If a type 2 SPD will suffice, Wylex seem to have a solution: https://www.tlc-direct.co.uk/Products/WYREC2SPD.html

   - Andy.
StuartBa
7 Posts
One main switch and 6 30mA rcbo's
Sparkingchip
2675 Posts
Then leaving the old ELCB as a main isolator can be considered acceptable, though a tadge scruffy.

There's things to consider regards earth fault protection between the tails, main switch, busbars and the metal enclosure of the CU, replacing the ELCB with a suitable RCD in a plastic enclosure has a lot of merit or a suitable double pole RCD as the main switch within the consumer unit..

Andy B.
StuartBa
7 Posts
My original question asked if l could use the elcb (with earth cables removed) as the isolator switch prior to the CU or do I need to remove it and fit a standard isolator switch. I already know that the main earth electrode cable and the water/gas bonding cables require upgrading.
Sparkingchip
2675 Posts
Sparkingchip:
Then leaving the old ELCB as a main isolator can be considered acceptable, though a tadge scruffy.

There's things to consider regards earth fault protection between the tails, main switch, busbars and the metal enclosure of the CU, replacing the ELCB with a suitable RCD in a plastic enclosure has a lot of merit or a suitable double pole RCD as the main switch within the consumer unit..

Andy B.


Yes it will function as a main switch, but there won't be any earth fault protection to the tails coming out of it, so give it a bit of thought.

StuartBa
7 Posts
Cheers Andy
Simon Barker
665 Posts
Dare I ask...

What's the advantage in removing the earth wires from the ELCB?
mapj1
2170 Posts
well it may reduce the risk of it tripping during thundersorms, or faults on adjacent properties.
Sparkingchip
2675 Posts
I have seen it done a fair few times, but haven't done it myself.

Andy B.
StuartBa
7 Posts
Basically the elcb is to be removed as its type Bs842 no longer confirms to regulations. I am removing the old wylex fuse board and replacing it with a new CU with individual rcbo's. My question was rather than remove the obsolete elcb could I use it as an isolator switch 
Alan Capon
368 Posts
What is the resistance of your earth rod? With six 30mA RCBOs and no overall RCD, your worst case leakage before anything trips could be as much as 180mA. That give you a max permissible earth rod resistance of 277 ohms to keep the touch voltage below 50V under normal circumstances. Ideally, you will want it much less than that. 

Regards,

Alan. 
gkenyon
1081 Posts
StuartBa:
Basically the elcb is to be removed as its type Bs842 no longer confirms to regulations. I am removing the old wylex fuse board and replacing it with a new CU with individual rcbo's. My question was rather than remove the obsolete elcb could I use it as an isolator switch 

BS 842 is not listed in Table 537.4, and therefore it's not easy to determine whether the device complies with Regulation Group 537.2 in the 18th Edition. One particular issue is that BS 842 doesn't explicitly state that the device is suitable for isolation, but this could perhaps be inferred by other wording in the standard, and it requiring the ELCB also complies with other product standards that may be suitable for isolation (but also are not listed in the current 18th Edition for that purpose).

However, I do know that a BS 824 device is only specified for prospective fault currents of 3 kA (if working to the standard - although I guess a particular manufacturer may have chosen a higher rating). If the supply has been upgraded from its original demand in the past, or will be in the future, that rating could be exceeded. (See ENA Engineering Recommendation P25 for further information - it's common these days, to simplify designs and purchasing requirements consumer units and associated equipment, to assume single-phase installations up to 100 A might be subject to 16 kA prospective short circuit currents.)

StuartBa
7 Posts
Alan l havent measured that yet the job l discuss is not yet started. Im just asking people's advise. In stead of installing an isolator switch im proposing that I fit a time delayed RCD. Thank you for your comments.
UKPN
127 Posts
You have no choice, it has to be an up front time delay rcd. Unless the DNO provide an earth facility.

Regards, UKPN⚡

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