Wiring in Live Systems

We are going to carry out wiring from live +24VDC system to our PLC system. We are being forced to carry out this operation with out shutdown. Can anyone give me exact references of IEC or other standards (that live wiring is against instrument and personal safety)? We wan to put these references in front of management and customers to take proper shutdown during wiring.

Waiting for an exact response.

It's not unreasonable to expect you to work on live 24 VDC, electricians work on live wiring all the time. All it takes is careful planning to avoid short circuit, etc. and the right protective wear.

If the source of 24 V is a battery, bear in mind the potential short circuit current is very high.
Perhaps you could add additional fuses or circuit breakers to the supply so that in future you can isolate different sections of the wiring without having to take a total shutdown.

Having said all that if you really believe it is unsafe you shouldn't work on it.

Roy

Your message is difficult to understand. Are you in fact the technical expert entrusted by the owner to maintain/support and now it looks like - modify the system? Then why do you need external authorities paperwork. You are the authority on the ground. You know the system functions - and outcomes of errors in wiring, unexpected loss of power, unplanned logic conditions etc. On a 24V system it will be difficult to argue from a personal safety point of view, the controlled system malfunctioning is what I would concentrate on.

Hugo

If you are only exposed to 24V it is not an issue. In the US, I think the standard is 60V. Even above that with a proper arc flash analysis and the right safety gear it is sometimes permitted.

"wiring from live +24VDC system to our PLC system... exact references of IEC or other standards that live wiring is against instrument and personal safety?"

NFPA 79 2007 clearly has provisions for working on live circuits. e.g. "6.2.3.1* Means shall be permitted to be provided for qualified persons, using appropriate work practices, to gain access without removing power."

The asterisk in there tells you to refer to "NFPA 70E, Standard for Electrical Safety in the Workplace." I have a hard-copy around here somewhere but I didn't feel like digging it out. Sorry. Also, the 2009 edition is coming out on Sept 9, 2008, and I don't know when a PDF version will be available.

24VDC is generally considered to be safe to work on. It is in a bit of a gray area; NFPA 79 says that 60 volts and less is fine if you're not around lots of water and you can't press your whole body up against live circuits. Less than 15 volts is essentially considered harmless. 24 volts is in between, so not harmless but not overly dangerous, either.

I don't know about IEC or UL. UL has some pretty restrictive policies regarding arc flash hazards when working in live panels.

If all you've got to worry about is 24VDC, I'd be more concerned about shorting out a component than I would be about getting hurt.

To your point, however, the RIGHT way to do this is to lock out ALL SOURCES OF ENERGY, including 24VDC, falling rocks, and Red Bull.

-James Ingraham
Sage Automation, Inc.

Do you really need an IEC reference to explain the inherent dangers of working on a live system? Isn't it part of your company policy not to work on live equipment?

Having said that, I am of the belief that sometimes--not all the time, but in some circumstances--it's necessary to work on live equipment. Troubleshooting can be extremely difficult when the system is de-energized. I'm basically referring to troubleshooting, but, depending on the available short circuit fault currents involved if there were a problem with whatever it is you're doing, it might be prudent to work on the system de-energized, or with a shutdown to avoid a forced shutdown, or worse, avoidable damage.

I like to refer to our jobs as risk management. The more experience we have the better we (should be) are at managing risk. We don't have enough details to support your position, other than to say that it's not generally accepted safety practice to work on live equipment. We don't know what systems you will be working, or what the consequences of a problem are. That's what supervisors and managers get paid to do: make decisions, otherwise known as manage risk. Some are better than others. Many times we don't have access to all the factors involved in the risk management (decision making), and sometimes we just just have to suck it up and do what we're told. We may not like, but we may also learn a thing or two in the process. Hopefully, it's not a negative lesson but a positive one, with a positive outcome.

Perhaps you are uncomfortable with the level of planning for this task; make your supervisor aware of your concerns. Suggest alternatives. When asked, or if appropriate if you believe the supervisor is not aware of all the potential risks (not just the human ones which should be first and foremost in their minds) then find a positive way to improve awareness. Have you tried proposing a meeting or two to discuss all the aspects of the work in question, outlining the risks and the plans for avoiding the risks as much as possible. Perhaps when they see things on paper, they might reconsider their plans.

When all else fails, you can choose not to do the work. Maybe the job isn't a good fit, and the risks are not worth the rewards. We all have to make those decisions, sometimes when we don't want to or can't really live with the consequences. It's your life; you need to do what you need to do to protect your life. If you're worried about plant, don't be; it doesn't seem the supervisors are. If you're worried about the lives of your fellow workers, that's admirable. Perhaps you need to make them aware of risks they may not be aware of, and let them make their own decisions.

Or, maybe your supervisors' acceptable level of risk is just greater than yours. I've watched (with more than little personal satisfaction in a couple of instances) more than a couple high-level risk takers take falls, all the while looking out for my own safety and dutifully trying to point out the risks I didn't think were being afforded enough weight in the decision-making.

There is also an old saying: We weren't given necks to never stick them out once in a while (it might lose something in the translation, but, it means we need to take some risks once in a while).

Friend, we don't have all the facts and we don't know your situation. All we can say is, use your head and pay attention to your heart, and practice as much safety as you can. No law or regulation is going to protect your life like you can.

Hi,

I think you'll find that Nürnberg put an end to that; you are responsible for your own actions. Most jurisdictions will prosecute the the actor, as well as the director.

I turn work down on a regular basis, because a potential customer will not agree to the mandated work required when modifying equipment.

Marc Sinclair

It is not the 24V that is dangerous. It is the 24v relay moving a 28 ton piece of equipment because it got wired wrong and the code did something unintentional because you did not have a "check-out".

Dave Ferguson

Exactly, I was wondering when someone would come out with that!

If you're working live, no doubt certain interlocks may be linked out which reduces the safety of the system as a whole. Machinery could start without warning causing injury to others working or damage to equipment.

Similarly, if whilst working live you managed to blow a power supply or something, the resulting outage could cost them a lot more than a planned
shutdown!

I would not disagree with that, however, it was not what the OP asked about.

Marc Sinclair, disagreeing with CSA's post:
"...you are responsible for your own actions."

Marc, I have to say that CSA made EXACTLY this point. I think you misinterpreted his post. He did say that there is such a thing as an acceptable level of risk, but you have to personally take responsibility for it. Even though he mentions that managers and directors should be doing risk assessment (and they should!) he talks about bringing things to their attention and then finally walking away if necessary.

Perhaps your quarrel is with the "risk" part. In which case, why don't we all just stay home in bed? We'd be much safer. And while seat belts are required in cars (except in New Hampshire), why don't we all wear helmets and 5-point harnesses like race car drivers? There IS such a thing as an acceptable level of risk.

In any case, comparing doing a task for work you consider dangerous to Nazi atrocities is not a helpful way to get your point across.

-James Ingraham
Sage Automation, Inc.

First do you mean by OP ? (brain fade on my part)

Second it does not matter what they asked for it matters what you are willing to risk to take the project.

Dave Ferguson

Hi, If you google 'nuremberg defence' I think you will find that it refers to a commonly used legal defence, namely _'I was told to do it, so I am not responsible.'_ The original poster mentioned that he was being told to do something which he felt could be dangerous, and cause harm to himself, or others, so the reference to this defence is entirely relevant.

As for avoiding risk , I agree this can be taken too far, if every single consequence of every single action is avoided, much like political correctness can make discussion difficult, if every connotation of every word is avoided, (or labelled not helpful).

Babies and bathwater are involved here too, the experience here in Europe is that industrial injuries and diseases continue to fall (relative to activity). Much of this is due to workers understanding their right to refuse to undertake tasks in a manner which they consider to be risky.

So where does this leave us? Well, I will continue to put on my harness and hat over x metres, and follow other Health and Safety rules, even where I can't see the risk, because I understand that my safety probably cost someone else dearly.

Marc Sinclair

Marc Sinclair:
"...a commonly used legal defence, namely _'I was told to do it, so I am not responsible.'_"

I re-read the entire thread. There is exactly ONE comment that even remotely resembles this excuse. CSA:
"Many times we don't have access to all the factors involved in the risk management (decision making), and sometimes we just just have to suck it up and do what we're told."

But to equate the two statements is taking CSA's horribly out of context. He ends with "...use your head and pay attention to your heart, and practice as much safety as you can. No law or regulation is going to protect your life like you can."

That's the OPPOSITE of "follow orders and you're not responsible."

Marc Sinclair:
"The original poster mentioned that he was being told to do something which he felt could be dangerous, and cause harm to himself, or others, so the reference to this defence is entirely relevant."

Except, again, he's doing the opposite. He's trying to get all his facts together to change the situation. He's even going so far as to try and call in outside experts. (I'm afraid we haven't been terribly helpful to him.) So where in any of this has anyone suggested that the original poster can abdicate resonsibility for his own safety?

>As for avoiding risk , I agree this can
>be taken too far, if every single
>consequence of every single action is
>avoided, much like political
>correctness can make discussion
>difficult, if every connotation of
>every word is avoided, (or labelled not
>helpful).

Ouch. Nicely done.

-James Ingraham
Sage Automation, Inc.

I can't offer an opinion as to whether the situation for the original poster was "safe" or not, as I have no direct knowledge of what the hazards might be.

However, with regards to risk and safety, in some countries at least it is illegal, leading to imprisonment, to undertake unsafe activities in the workplace whether someone is injured or not. It may in fact be an offence to simply put a machine into operation after modifying it without first having it inspected and approved by a competent authority.

For the benefit of the original poster, I would suggest that you identify what the hazards might be. These might include dangers to the personnel conducting the work, dangers to others working in the area if the equipment malfunctions while or as a result of being worked on, and finally the risk of damage to the equipment itself. Errors are highly likely to occur given the conditions the work is being conducted under. The question then is what the possible consequences could be.

OP=original poster.

If I recall correctly (IIRC) the OP seemed more concerned with electrical hazards associated with live work rather than equipment damage.

Despite the derailing of your topic, I think some points are clear...

Legal Safety Standards are dependent on your country's legislation. However, the actual connecting & disconnecting of a 24 Volt DC power source is unlikely to endanger anyone's life under normal circumstances.

Your problem really boils down to under qualified production & and management instructing you to do work that you are uncomfortable with.

In this case, the risk is likely to be that you cause a short which will damage equipment, which will shut the plant - or simply make mistakes in the wiring.

To justify your refusal to perform this work, you may want to analyse the risk and cost associated with your control system either shutting down entirely, or a critical part of the process starting/stopping in an uncontrolled manner.

The results of this may be financial or safety related or typically both. I would hope that your existing plant already has a safe work practice scheme of some description which allows you to complete this analysis.

If it doesn't, then you have a much bigger problem.

My 2c

www[.]lymac.co.nz

I would venture to say that the original poster didn't get quite the reaction he anticipated, and so we'll never hear exactly what his concerns were. We don't know what kind of work or processes are done at the site; we just didn't have a lot of information to go on.

This smacks of management/supervision steadfastly adhering to a safety policy and then, at their convenience, deciding to make an exception without reviewing the work to be done and the effects of any unanticipated issues. I think most of agree that 24 VDC is relatively benign (and we don't know about the source or the extent of the work, so that's a presumption in this case) and any and all electrical work has inherent dangers of one sort or another (I've seen people cut by poorly installed plastic wire ties develop a serious local infection!).

But, I would agree with Dave Ferguson's statement that it's not the 24 VDC that's the dangerous part of the work that's being proposed be done "live"; it's the effects of a possible miswiring or even the loss of the entire control system because of a dropped wire that came in contact with ground or shorted out the power supply.

But, again, we'll likely never know all the details.

Interesting conversation the original poster "sparked", though! (Pun intended!)