The obvious conclusion is that their is no regulation to prohibit it.
From a Health and Safety point of view, does this not make you wonder...if not, why not? If it was known to be the direct cause of peoples' deaths, surely they would have prohibited it by now?
I have spoken to our 2 uk panel shops who say they cannot understand why it would be done like that because it is not considered 'good practice' or 'normal' however their is no requirement/ regulation.
Again, I'm seeing the
belief, but not the reason?
Just because they
cannot understand why, does not automatically make it dangerous.
It's
not considered 'good practice'. Did you ask them why, did they say why?
It's always good to seek council, as you have done here. But, no matter how many people tell you what is
considered right or wrong,
normal or abnormal, you should decide for yourself.
I am possibly in the minority, on the whole, but I still choose to believe what I think makes most sense,
from a Health and Safety point of view.
I keep using that statement, it's important I do. It's so you are constantly aware of the distinction I'm making here between whether you should use this method of wiring or not with regard to safety of life, and not with regard to preferred wiring methods for aesthetics.
All I'm asking you to do here is question your, so far undisclosed, reasons for believing it is dangerous.
The MCB drawings/layouts SHOULD reflect the panel... why bother at all if they don't? A panel layout/GA and a set of drawings should contain enough data to allow a duplication of the panel.
When done correctly, wiring and layout schematics, do reflect the panel, accurately. Even using the 2,4,6 example I mentioned.
Wiring schematics for MCBs or any other components, do not use layout to denote what wire goes where, they use terminal numbering and/or wire numbering, along with symbols. The symbol denotes what component the wire is associated with and the terminal number denotes where the wire is terminated on that component.
Q: What terminal number do I need to put this wire in?
A: schematics> '1' on 'MCB1'
Find terminal 1 on MCB1 and terminate it there. If it's on the bottom of something or the top it doesn't matter, that's where the schematics have told you to terminate it. You don't put it on the top, just because it is shown that way in the drawings, you follow the terminal numbers.
Layout, or
General Arrangement,
schematics are just that, general. They denote the position of components within a panel, and they identify them. They don't tell you if component A is fed physically to the top or bottom, they usually don't show any wiring.
To wire a duplicate panel, you layout the components as per the GA. You wire those components as per the terminal numbering in the wiring schematics.
You don't expect wiring or layout schematics to reflect the physical layout of each wire and the orientation of each contact? That would be too verbose, and unnecessary, at least in most cases.
For instance, often in wiring schematics you might see a wire come from above to a terminal on a relay numbered, say, '11'. When you look for '11' on the relay, it may very well be physically on the bottom of the relay. The wiring schematics don't need to map out the physical orientation of all the wires and contacts. The lines that represent wires in a wiring schematics are pointers from one terminal to the next, that's all.
Often, two identical panels, wired by two separate people, using the same wiring schematics, will differ a lot in how the wires were routed from A to B. Some wires between identical sets of terminals may differ greatly in length, depending on which route they took. You would not expect them to confer on exactly how each wire is routed from A to B.
So, you do not need schematics to show the supply wires going around and down to 2,4,6 on the bottom of the symbol for an MCB. You just put 2,4,6 on the top of the symbol.
Should I need to be explaining all this to you?
If I've somehow mis-read your point, forgive me.
I just had a customer on another site reject a drawing because the +/- terminals on the 24V PSU were opposite to the actual PSU.. very petty I would agree but it was quicker to re-draw than to argue.
I am particular with details, but this is a bit too fussy. Drawings are detailed guides, but do not need to be quite that accurate. It's their prerogative non the less. Was the - on the left of the +? I know that doesn't sit well with someone people.
The MCB's on the drawings show TOP fed (by nature of the layout) and also by the pin numbers of the MCB... which is why I would have rejected it if I was doing the panel sign off.
As I've said, wiring schematics are not layout schematics, so forget the 'nature of the layout'. However, if the wires coming from the
supply are shown terminated into 1,3,5 on the drawing, but are actually terminated to 2,4,6 (or whatever the numbering), then the drawings are not accurate to the wiring.
Now we're back to the decision...
If it's decided that the wiring is ok to be left as is, the wiring schematics need to be amended to place numbers 2,4,6 on top of each symbol and 1,3,5 on the bottom, that's all.
If your specification (is there one?) says the panel should have been wired as per the wiring schematics, or someone decides they want it changed, then the wiring needs to be changed.
At the end of the day if we stick to regulations, the power should be OFF if the door is open so it is not a safety issue.. however we all know that will not be the case
Your right, it wont always be the case.
Regulations and safe practices do not stipulate the power must be off before opening the door.
Many panel door isolators are defeatable and permissible. Depending on the work being carried out, it is fine to have the door open with power on. You may be resetting a breaker without powering down the whole panel, or you may be live testing for a fault, or commissioning.
But, if you are isolating the panel to carry out work with the potential for direct contact with live parts, it is still a safety issue after the panel is isolated, until you check for voltage at the point of work.
Isolating a panel and proceeding to work on and around live parts, with the
assumption that it is dead, is not safe practice.
I am going to have to spend 2-3 site days in the eye of the customer red lining the drawings so the already checked 'AS BUILTS' can be updated to be true 'AS BUILTS' which does not build any confidence with the customer and keeps me from my family due to imcompetence which basically P!sses me off
Aside from my crusade here,
Remember, I have never said that you should or should not accept this panel. I have only outlined where you should stand, and that you cannot argue the case, to have it changed, based on it being dangerous, it is not. It's whether or not your company allows it. That decision still has to be made. Or perhaps its already been made, you just don't know it yet?
JesperMP,
Thank you for the feedback on HV testing.
It is more dangerous than the top supply because it is not the typical practice. But I dont think there are regulations against it.And there will always be cases where you have a special dangerous situation.
If people
always test for voltage before they work on any circuit, how is it especially dangerous? It's the same supply your verifying is off? It won't kill you any less just because it's on the bottom of the breaker!
My real fear is, not using it because it is perceived as dangerous, not good practice, abnormal, atypical, irregular, uncommon, creates some sense of false safety. Once someone assumes it isn't there, they are somehow safer from the same potential voltage. Also, it indicates to me, that once it is assumed not there, the danger from the complacency of not verifying first is exponentially greater.
The real issue here is, too many people are complacent, and want to rely on this method to somehow protect them from the very danger that will always be present, no matter which way you bend it.
Be safe!
G.
