RCD over rated ?

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Thunderchild

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Hi guys I've just moved into a house with a new fuse box but the RCD is 100mA, surely this should be 30 mA as after that your err...... DEAD ?
 
Also know as a GFI or Ground Fault Interrupter.
 
Even 30ma seems a bit high. Our NEC code is around 6ma.


National Electrical Code - Wikipedia, the free encyclopedia
 
Well there will be some natural discharge to ground throughout the system but I think 100 mA is far too much, I've always seen 30mA and yes it has saved my life
 
Thunderchild said:
Well there will be some natural discharge to ground throughout the system but I think 100 mA is far too much, I've always seen 30mA and yes it has saved my life
Click to expand...

hi TC,
Look thru this pdf.

EDIT:
Basically the RCD rating is analogous to domestic fuse ratings, the mains entry point has much higher fuse rating than the auxiliary outlet fuses, this avoids the whole house power being cut off when an auxiliary device fails.
The primary RCD is rated at 100mA and the auxiliary RCD's should be 30mA or 6mA, this again avoids a full house power off when an auxiliary device is triggered.
 

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Also note (as you are in the UK) that the 17th edition wiring rules changed some things for RCDs. Mostly for the better I understand, but I am not an electrician.

I have a split board: 30mA RCD for outdoors & the shower and no RCD on the other half (it was installed a long time ago).
 

Ah yes but it is the only RCD on the board so a little worrying
 
Thunderchild said:
Ah yes but it is the only RCD on the board so a little worrying
Click to expand...

Not really, it depends when it was fitted - as Eric says, 100mA for the primary is fairly normal. I've only got a primary RCD in my house, but I've no idea what it's value might be? (but it's far more sensitive than the antique one it replaced).
 
Nigel Goodwin said:
Not really, it depends when it was fitted - as Eric says, 100mA for the primary is fairly normal. I've only got a primary RCD in my house, but I've no idea what it's value might be? (but it's far more sensitive than the antique one it replaced).
Click to expand...

well I can understand having a main RCD rated high so as to not trip the whole house when a smaller one goes but there are no smaller ones, this one is rated at 63 A so indeed is the main one but there are no smaller ones, i suspect the house was wired by an amateur, as far as i know 30 mA will kill a person so 100mA surfices to say this house has RCD protection but it does not really help. if it was followed by a series of 30 mA RCD's I'd understand but there are non.
 

How many people have been electrocuted in the house? - just a single RCD (or no RCD at all) is perfectly OK, both were the official standard at their time.
 
well this looks like a recent installation, the old fuse box is still there in fact left disconnected. My view is that I should remember that yea I have an RCD but NO this will not really be of much use in the event of potential electrocution. My point is that it is obvious that the house has been given a makeover by a bodger, I have found original electric wires cut off and left in the light switch and the decorating and general repairs done to the house is somewhat what I'd expect of a bodger like skirting board around the door frame to hide the fact that he did not want to plaster around the door he replaced. when entering as new house I treat anything with suspicion, better find out quickly what it's about and fix it before i get everything sorted rather than have to fix it once i have moved in with new carpets and decorating done, i know that I jolly well felt it when I blew the 30mA RCD (with lots of leakage in the circuit) I'm pretty sure 100mA would cut out after I'm dead
 

It takes a LOT to kill someone, you have to work pretty hard at it - or be REALLY, REALLY unlucky

If you're not happy with it, then change it - but presumably you'll need a professional electrian unless you're going to 'bodge it'?.
 
well the difference between me bodging it and someone else bodging it is that I'll put my hand up and ask for advice before ploughing in. I mean for starters I have to sort out the cables from the old box from the cables for the new box. had I done it i would have removed the old box which is actually totally disconnected I believe.

As professional electricians self certify their work I think I'd prefer to self certify mine, I've done my own wiring before, nothing new there
 
well in canada there no main rcd on breaker boxes, i fact the only place where we install rcd are near shower or spa and pools and outdoor outlets. I already been electrocuted on 120V and i would have to have foot in water to get killed by so low voltage
 
Nigel Goodwin said:
It takes a LOT to kill someone, you have to work pretty hard at it - or be REALLY, REALLY unlucky

If you're not happy with it, then change it - but presumably you'll need a professional electrian unless you're going to 'bodge it'?.
Click to expand...

It has been thirty years since electronics classes, and any discussion of what constitutes deadly amounts of current, but 100 mA to 200 mA was quoted as killer range. Anything less than 100 mA wouldn't stop the heart, and anything greater would sieze up the heart, but with no ill effect if the source was removed quickly. The range mentioned is where the heart goes into defibrillation, which continues to be a problem after the shock source is removed. In the States, IIRC, GFIs are set to trigger at, or less than, 10 mA.

So, it doesn't take A LOT to kill you, but a lot will definitely do you in.

If this has changed, I'd sure like to hear about it.
 
Well really I don't quite see the need for a main RCD unless there is no main fuse. If every circuit has an RCD there should be no need for a main one
 

Nothing has changed, but you need the current to flow through you -you don't easily get those high currents flowing through a body.

Like I said, it takes a good bit of work (or bad luck) to be killed by 240V.
 

If you're fiddling with the fusebox it now needs to be done professionally and certified - no electrian is likely to certifiy work they haven't done - for you to certify it yourself, you will have to gain the relevent qualifications.
 
yea I meant that I'd rather do the work myself and be satisfied that I've done it correctly than have an electrician come in and do it and be able to say that he did a good job and charge me a fortune for what I can do myself anyhow.

I was always taught that 30 mA was the limit for humans and that it corresponded to 30/40 volts which is also considered the safety voltage, of course circumstances will vary, my dad's uncle had 20'000 volts go through him and survived but safety is not about "buts" and "ifs" it's about making sure it just remotely never occurs.

Like i said i suspect this box was not installed by an electrician anyway and if it was I would rather not see him "practicing" on anyone else's wiring.
 
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