This guy is about to start his NVQ3.
//www.diynot.com/forums/viewtopic.php?t=282446&start=0
Is the course going to work miracles?
A bit of bondage!
- Thread starter dingbat
- Start date
- Status
//www.diynot.com/forums/viewtopic.php?t=282446&start=0
Is the course going to work miracles?
Sponsored Links
Great! just read the thread. cmossom has single handedly undermined any confidence I had that things will improve. He appears not to have even a basic education
Is an RCBO not an RCD (and MCB in a single package)?
Essentially yes but some (or all) RCBOs conforming to BS/EN61009 offer a maximum disconnection time of 300Ms at 1X I-delta-N as I understand it.
Is an RCBO not an RCD (and MCB in a single package)?
Essentially yes but some (or all) RCBOs conforming to BS/EN61009 offer a maximum disconnection time of 300mS at 1X I-delta-N as I understand it.
Sponsored Links
That is the maximum allowed time for 61008/9 RCDs (non time-delayed)
@ 1x 300ms
@ 5x 40ms
Although, of course, normally less.
Yes, I was making the point to Mr Cockburn that you can't make assumptions about earth leakage disconnection times (or any disconnection time for that matter)
He simplistically wrote (and I quote)
"Firstly Sparticus - the RCD trips within 0.04 of a second"
Yes, that is my experience with them too. In general I never see any significant difference during 1X tests between an RCD and an RCBO but I thought it relevant to raise the possibility.
Sorry, I didn't realise the point you were making.
Indeed it can. It can also make it better. One has to think about the specific situation and make a intelligent judgement as to which is the greater of opposing risks. To generalise is not, IMO, wise.
Indeed you can't, but you have to make a judgement as to which scenarios and which types of stupidity may arise, and which are the more likely. It seems that you and I have come to different decisions in the specific scenario I described; that's fine, and doesn't mean that either of us is 'right' or 'wrong'. If there was a claer 'right' and 'wrong', we wouldn't be having this discussion.
Kind Regards, John
I wasn't planning for both. I was considering both and then 'designing' on the basis of the one I, IMO, regarded as more likely (even though very unlikely).
Did I not describe the specific hypothetical scenaio clearly enough? I said that there was no electrical installation anywhere near the bath. In that situation, there would (in the absence of stupidity with extension leads) be no faulty appliance to have a frayed lead. I would therefore regard the possibility of your second scenario as essentially zero, so the first one, even if it had 'hardly any liklihood', would still have more liklihood than the second.
Kind Regards, John
This is where you are going wrong.
There is no difference between a metal table and an isolated bath (or sink, or even BAS' spoon).
It would be less safe if the table were bonded.
If it were an electric table which could become live because of a fault then it would be earthed (or double insulated).
This could be a vacuum cleaner, floor polisher or even a tool being used for repair work in the bathroom.
In case I am missing your point completely, what electrical installation may be near the bath?
OK, yes, I concede that; I was only thinking of what went on when the bathroom was being used as a bathroom.
Kind Regards, John.
Fair enough.
In passing, I think this illustrates how the distinction between earthing and bonding gets a bit confused. Before anyone tries yet again to tell me that I don't understand the difference, let me assure them that I do understand the difference between the purposes of earthing and bonding. However, when you say that the table would be less safe if it were bonded, the reason you say that is not because it would (if bonded) be equipotential with other metallic parts (the purpose of bonding) but, rather, because that bonding would indirectly provide a path to earth. The hazard to which you refer therefore would arise because the bonding would actually 'earth' the table.
I'm starting to wonder whether you believe in the concept of any supplementary bonding. If all required main protective bonding is in place, it would seem that there are only two possibilities for any metallic part within the premises - either it is already (deliberately or otherwise) effectively bonded to MET/CPCs, in which case there's no point in adding supplementary bonding OR it is not connected to the MET/CPC (or anything else to do with the electrical installation!!), in which case it is floating and therefore, per what you have said, should not be bonded. In the presence of satisfactory MPB, there is no way I can think of that it could 'introduce a potential' other than (if so connected) that of the the MET/CPCs.
Kind Regards, John.
Me neither, I thought RCD was just a generic term which includes RCCBs, RCBOs, SRCDs etc.
A RCCB being what most people refer to as an RCD.
Spark123, you are right I think "RCD" is or has become a generic term. I was trying to get Mr Cockburn to realise/acknowledge that you can not make assumptions about disconnection times, that the actual disconnection times are dependant upon the device, the wiring, the "impedance" of the earth fault That a fatal electric shock could be received within the disconnection time.
I got the impression from his comment that all is fine, the RCD will disconnect within 0.04 seconds. I do not hold such faith in these devices and think of them as last resorts rather than a fix-all for poor electrical design. I probably should have written this at the time but I was being intentionally "difficult"
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
- Status
Sponsored Links
Similar threads
- dextrous
- Plumbing and Central Heating
