Time delayed trip
- Thread starter Deansplit
- Start date
An electrician who quoted on rewiring our kitchen which was extended. All power has been coiled back to the door to it so will be a total rewire as new layout, bigger room, more appliances etc. Said it's best to give it its own consumer unit. It's a fair size room, 47m2 and power from the new consumer unit will also power garage and utility rm.
It sounds like your electrician is just recommending you have a sub main installed for your extension which can have a 5 secs disconnection time opposed to the 0.4 secs for final circuits, nothing wrong with that.
Well that's a whole lot o help... what's that mean??
Sorry It was a comment for discussion by the sparks I am sorry I had read your post a bit quick, a time delayed RCD I would normally use if there is no suppliers earth IE a farm, remote house etc you would need to know the tripping current of you TD RCD IE 100 amp is the load and 30mA trip, on a TD it is usually but not always a 100mA trip but it all depends on your specific situation are you out in the sticks, I would need a lot more info about your supply set up,But I would not loose any sleep over it just ask you spark some questions most of us will be quite happy to explain mind you there are some grumpy old sods out there
DM
DM
T
tonyelectric
We routinely use time delayed RCDs in commercial buildings where you have sub-mains or subsidiary distribution boards, The local board is protected by a 30mA standard RCD, the cable between the main board and the sub board is protected by a 100mA time delayed RCD, this gives a degree of protection by ADS (automatic disconnection of supply) to the cable whilst the standard RCD protects the final circuits.
This arrangement gives discrimination, meaning that you cutting the flex of your electric carving knife will trip the breaker at the local board, not the main board so you can reset locally. If you had two standard RCDs they would trip in harmony so you would have to walk back to the main board.
Not that common in houses, but nothing wrong with it, they are however pricey, last one I purchased was best part of £100
This arrangement gives discrimination, meaning that you cutting the flex of your electric carving knife will trip the breaker at the local board, not the main board so you can reset locally. If you had two standard RCDs they would trip in harmony so you would have to walk back to the main board.
Not that common in houses, but nothing wrong with it, they are however pricey, last one I purchased was best part of £100
A bit pointless really as it is not required...
To the OP - do you live in rural area or know if your earth is achieved by means of an earth rod. A picture of your mains position would be useful
T
tonyelectric
Agreed, but a requirement in council owned school premises round here, one of many odd ideas - but it has saved life once when a caetaker hacked through a 25mm2 SWA thinking it was dead - by rights it shouldn't have saved him but it did.
I've tried leaving it off a few drawings but it always gets added in by the electrical consulting engineers
I've tried leaving it off a few drawings but it always gets added in by the electrical consulting engineers
No, live in a town, it's a large Victorian home, rewired 15 yrs ago. it has 3 boards as was a B&B so lots of elec shows, water heaters etc. When u say a picture, u mean map of where it is?... kitchen is a rear of house, 12m from porch where the mains in/boards are.
T
tonyelectric
Have a look at your mains, there will be a fat cable coming in from either the ground or overhead, this connects to a black or grey bakelite fuse unit that is commonly called a cut out, it may have the name Henley or Lucy or ISCO on it.
Look for your main earth, the biggest of the green yellow wires, it will do one of 3 things.
Be clamped to the outside of the incoming cable , thats TNS
Go into the black box , thats TNC-S, there may also be a label mentioning PME
Go outside to a rod in the ground, thats TT
If the black box has just one protruding cover sealed with wire then you have single ph.
If it has 2 you have split ph
or 3 its 3 phase
Incidently don't attempt to open or look inside that box, it should never be interfered with
Look for your main earth, the biggest of the green yellow wires, it will do one of 3 things.
Be clamped to the outside of the incoming cable , thats TNS
Go into the black box , thats TNC-S, there may also be a label mentioning PME
Go outside to a rod in the ground, thats TT
If the black box has just one protruding cover sealed with wire then you have single ph.
If it has 2 you have split ph
or 3 its 3 phase
Incidently don't attempt to open or look inside that box, it should never be interfered with
And I bet it was last thing on a friday evening as well? "I'll just grab this redudant cable to way in after everyone else has gone home"
Actually I'm not sure the RCD would have made much difference, the hacksaw blade is earthed via the armouring its just cut through first, the hazard here is from arc flash rather than electrocution, as its the fault touch voltage thats present, rather than Uo, and hes probably standing on a roof top or holding the wooden handle of the saw anyway. Assuming the overcurrent device was a MCCB, (or if it was a fuse, that the disconnection time was closer to 0.4 than 5s) then it should have beaten the RCD anyway.
Be a nice shower of sparks and a WTF moment though
Anyway, I hope that at the far end of these submains with time delayed RCDs on at source, that you are not using DBs incorpationg RCBOs which only break the phase conductor...
And does the consultant sign for design on your EIC
Dean, No we mean a photograph of your fuseboard, service intake and metering equipment
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