Discuss Anyone know of any manufactures of small recessed DB's or any other options? in the Electrical Forum area at ElectriciansForums.net

J

JohnS888

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The new devices are approximately 8mm taller through the board cover. Dimensionally when on the DIN rail they seem okay. Whether they are compatible with that enclosure in compliance with Regulations is another thing.View attachment 60813View attachment 60814View attachment 60815
Top man Westward. I'll have to check whether have the 8mm to spare. It's more likely that will go with RCBO's so hopefully these won't be much bigger. Don't suppose you have one of those as well do you? 🤣
 
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westward10

westward10

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No but the dimensions should be the same except the rcbo will be longer which could be an issue.
 
freddo

freddo

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Arms
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I'd still enlarge opening to accommodate new box it's going to take you half an hour or so to do it.
I'd also go with this for the amendment 3 thing, assuming the existing cover is plastic. I'm not sure if mixing different devices and enclosures is allowed.
 
J

JohnS888

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I'd also go with this for the amendment 3 thing, assuming the existing cover is plastic. I'm not sure if mixing different devices and enclosures is allowed.
It is metallic freddo. I hear you with covering arse with mixing enclosure but just seems to be a non issue in my opinion if din tails are all made to a certain spec and fit both same spec main switch and rcbos surely we have pretty much not changed any other important characteristics of a pre manufactured board
 
J

JohnS888

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Another query for you's. I haven't had a chance to check out supply type for property yet so there is a possibility it could be a TT earthing arrangement although very much doubt it. I find the fact that they installed a 300ma main switch pretty strange. Has 300ma circuit protection ever been a requirement in previous regs? And also as my DB is only supplying a residential property with no distribution circuits or essential services am i correct in thinking even if is a TT installation 30ma rcbos or 30ma main switch would be appropriate? I can't see why it wouldn't be. Thanks
 
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pc1966

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Having an RCD up-front above 30mA is usually a TT thing, or sometimes a fire safety for agriculture sites. 100mA is more common for domestic, but 300mA is just as acceptable provided the earth rod is below 167 ohms.

I don't think there ever has been a requirement on 30mA / 100mA / 300mA (or possibly more) as such. The main point has always been to meet ADS times and for TT that is often only possible via an RCD as you will struggle to get a rod arrangement low enough to trip even a 6A B MCB in the required times.

I suspect 100mA is the 'sweet spot' as less likely to nuisance trip than 30mA for a whole installation, and can had delay so it is selective with downstream 30mA 'additional protection' RCDs, whereas 300mA starts to demand an earth rod impedance that can be a challenge to meet all-year in some soil conditions without quite an effort for several deep rods, etc. Or the no-no of relying on a nice long buried metal water pipe...
 
J

JohnS888

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Having an RCD up-front above 30mA is usually a TT thing, or sometimes a fire safety for agriculture sites. 100mA is more common for domestic, but 300mA is just as acceptable provided the earth rod is below 167 ohms.

I don't think there ever has been a requirement on 30mA / 100mA / 300mA (or possibly more) as such. The main point has always been to meet ADS times and for TT that is often only possible via an RCD as you will struggle to get a rod arrangement low enough to trip even a 6A B MCB in the required times.

I suspect 100mA is the 'sweet spot' as less likely to nuisance trip than 30mA for a whole installation, and can had delay so it is selective with downstream 30mA 'additional protection' RCDs, whereas 300mA starts to demand an earth rod impedance that can be a challenge to meet all-year in some soil conditions without quite an effort for several deep rods, etc. Or the no-no of relying on a nice long buried metal water pipe...
Thanks for clarification PC so am right in thinking then if is a TT installation if either install dual rcd board with non rcd main switch or all rcbos I have still achieved the required disconnection times. Thank
 
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pc1966

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Thanks for clarification PC so am right in thinking then if is a TT installation if either install dual rcd board with non rcd main switch or all rcbos I have still achieved the required disconnection times. Thank
If all of your final circuits are off an RCD/MCB or RCBO then you would be able to meet the ADS times on any reasonable TT earth rod setup.

Personally I would still prefer an up-front delay RCD so you don't have a single point of failure for protection in something as complex as an RCD (which is normally seen as "additional protection" along with OCPD based primary ADS protection, and in practice don't get tested by the users), but it is not a requirement as such.
 
J

JohnS888

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If all of your final circuits are off an RCD/MCB or RCBO then you would be able to meet the ADS times on any reasonable TT earth rod setup.

Personally I would still prefer an up-front delay RCD so you don't have a single point of failure for protection in something as complex as an RCD (which is normally seen as "additional protection" along with OCPD based primary ADS protection, and in practice don't get tested by the users), but it is not a requirement as such.
Thanks PC very valid points. I think I'm with you on that thinking to
 
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