Isolation for maintenance

[TailSpin]

Hi All

not sure whether this question has been posted before so here goes :

An isolator on a control panel which feeds an inverter and on to the motor , the problem is when you turn off the isolator it does not kill all the panel some parts have a supply on them which then feed things like 230 volt fans ect .
I thought that once the isolate was off that should then kill the panel except my be for some control circuits.

any thoughts ?
regards
John

 

[Rockingit]

An isolator isolates whatever it's been designed to do, simple as, and should be labelled as such.

 

[Pete999]

Hi All

not sure whether this question has been posted before so here goes :

An isolator on a control panel which feeds an inverter and on to the motor , the problem is when you turn off the isolator it does not kill all the panel some parts have a supply on them which then feed things like 230 volt fans ect .
I thought that once the isolate was off that should then kill the panel except my be for some control circuits.

any thoughts ?
regards
John

What equipment are you going to work on? is there not a local isolator next to the equipment you intend to work on?

 

[Knobhead]

It’s a common problem and one you just have to get used to.

 

[Darkwood]

Hi All

not sure whether this question has been posted before so here goes :

An isolator on a control panel which feeds an inverter and on to the motor , the problem is when you turn off the isolator it does not kill all the panel some parts have a supply on them which then feed things like 230 volt fans ect .
I thought that once the isolate was off that should then kill the panel except my be for some control circuits.

any thoughts ?
regards
John

Most of the panels I work on and build are designed as such and sometimes for maintenance purposes, the cables connected that remain live when panel is opened should be orange and can feed many things like stopping software crashes, panel lights and sockets for the engineer etc ....the list goes on, this is common practice and what is wrong here is probably the misleading title of the thread, you are not isolating here you are switching off sections of the power and control to allow for maintenance. An Isolator upstream of the panel would be for safe Isolation of the whole machine. (Assuming its fed off one supply).

My question is; Why are you in the panel if you are unaware of the regulations and practices that govern them? They don't fall under the BS7671 although some regulations are repeated in the BS7671 so if you are an Electrician the most you should be doing in this panel is connecting the power supply to it, anything else and your insurance will probably be void.

 

[Robotstar5]

It should have a notice warning parts are still live with isolator off

 

[telectrix]

so get your sharpie out, then.

 

[Deleted member 26818]

Is this a case of one isolator controlling only part of a machine, or is it a machine with two supplies?
To my mind there should be an Isolator whereby the whole machine can be switched off.

 

[shanky887614]

this is a standard panel you will come across.

power on one side and controls on the other, the controls will be fed from the supply side of the isolater.

now depending on the panel there are ways to isolate it via relays,fuses etc.

you shouldnt be touching any of these if you don't know what you are doing.

the isolator on the front is not usually designed to conpletely isolate the panel

 

[shanky887614]

Is this a case of one isolator controlling only part of a machine, or is it a machine with two supplies?
To my mind there should be an Isolator whereby the whole machine can be switched off.

it sounds like a bms/controls panel mate with the inverter in the panel etc.

i doubt it serves a single machine, the panels we work on always stay live because they are continuously reporting back to the estates/maintenance department.

 

[TailSpin]

Most of the panels I work on and build are designed as such and sometimes for maintenance purposes, the cables connected that remain live when panel is opened should be orange and can feed many things like stopping software crashes, panel lights and sockets for the engineer etc ....the list goes on, this is common practice and what is wrong here is probably the misleading title of the thread, you are not isolating here you are switching off sections of the power and control to allow for maintenance. An Isolator upstream of the panel would be for safe Isolation of the whole machine. (Assuming its fed off one supply).

My question is; Why are you in the panel if you are unaware of the regulations and practices that govern them? They don't fall under the BS7671 although some regulations are repeated in the BS7671 so if you are an Electrician the most you should be doing in this panel is connecting the power supply to it, anything else and your insurance will probably be void.

I am in the panel doing maintenance works on the inverter , the main supply goes through a isolator but there is a multicore cable that feeds things like panel lights fans ect some are 230 volts so when the main isolator is off and they are very much on . I would just seem good practice to have these circuits isolated when the main switch is off . I guess it requires clear labels to warn of circuits still alive in panel when isolated .

 

[Darkwood]

I am in the panel doing maintenance works on the inverter , the main supply goes through a isolator but there is a multicore cable that feeds things like panel lights fans ect some are 230 volts so when the main isolator is off and they are very much on . I would just seem good practice to have these circuits isolated when the main switch is off . I guess it requires clear labels to warn of circuits still alive in panel when isolated .

Depends how old the panel is, any modern panel that meets requirements will be clearly labelled and usually have shields over any exposed connections that remain live or fingersafe at least with individual warnings, often common for power to run to an isolating Tx that feeds all the necessary's like maintenance lights and power etc, either way if your inside the panel you should still be knowledged in panel regulations and design so as not to put yourself at risk. If you hadn't noticed part of the system was still energised 'Its not always clear' then you could have been at risk of shock and the risk is higher with old panels that lack modern standards. Panel heaters are the most common requirement for tapping of the live side of the panel interlock, when the operator switches off the machine after his shift the panel still has protection from condensation.

I wasn't having a go at your competence just questioning it based on your query plus your lack of profile info so we have to ask; there are many hazards if you don't understand the practices and regulations of control systems regardless of you only making adjustments to say a VSD parameter.

 

[netblindpaul]

There are clear specifications for allowing circuits in a machine control panel to remain live after the main isolator is switched off.
It is common practice, and is in accordance with the BS EN standard for machinery panels.
It is also totally acceptable, and necessary.
There is no issue with this scenario.

 

[Deleted member 26818]

I belive there is an issue, if there is no warning that such is the case on a machine or panel that we have to work on or in.
I've seen isolators that should have been wired to BS7671 by-passed so as to provide power to parts of a machine even when the isolator is switched and locked off.

 

[shanky887614]

I belive there is an issue, if there is no warning that such is the case on a machine or panel that we have to work on or in.
I've seen isolators that should have been wired to BS7671 by-passed so as to provide power to parts of a machine even when the isolator is switched and locked off.

an isolator on the door of a control panel doesnt come under bs7671.

they usually say isolate elsewhere before opening

 

[silva.foxx]

I belive there is an issue, if there is no warning that such is the case on a machine or panel that we have to work on or in.
I've seen isolators that should have been wired to BS7671 by-passed so as to provide power to parts of a machine even when the isolator is switched and locked off.

Does the panel schematics show this setup as it is?

The panel auxiliary equipment should still have mcb/fuse protection for own isolation purposes... is this provided in this case?

s.f

 

[Deleted member 26818]

I thought that were discussing Isolation?
Not main switches on machinery or panels.
To my mind an Isolator positioned adjacent to the device it is intended for, should isolate all power, not just some of the power. The clue being in the name.
A main switch situated on the machine, or the panel is another matter.
Of course parts inside will still be live, the conductors that go to the main switch for instance.

 

[shanky887614]

I thought that were discussing Isolation?
Not main switches on machinery or panels.
To my mind an Isolator positioned adjacent to the device it is intended for, should isolate all power, not just some of the power. The clue being in the name.
A main switch situated on the machine, or the panel is another matter.
Of course parts inside will still be live, the conductors that go to the main switch for instance.

the op is talking about an isolator built in to the front of a control panel.

 

[Deleted member 26818]

Ah yes, so I see.
Crossed wires.

 

[Knobhead]

We always used MCC panels with withdrawable starters which will obviously totally isolate the individual starter once withdrawn, OK so far. At the heart of the MCC would be the marshalling cabinet. The control of every drive would go through it, along with links to other equipment. Short of turning the 11KV incoming to the plant off you had no chance of isolating everything. Even then, there’d be links to other plants.

You just had to get used to testing the bit you want to work on before sticking your pinkies in.

 

[shanky887614]

We always used MCC panels with withdrawable starters which will obviously totally isolate the individual starter once withdrawn, OK so far. At the heart of the MCC would be the marshalling cabinet. The control of every drive would go through it, along with links to other equipment. Short of turning the 11KV incoming to the plant off you had no chance of isolating everything. Even then, there’d be links to other plants.

You just had to get used to testing the bit you want to work on before sticking your pinkies in.

that is like what we do, the difference being we have to work live on some bms/door access or you will shut 10 doors or the whole floor down.

you try telling the already stretched security staff they need to secure 10-15 entraces to stop the loonies getting out

 

[Jamzie]

It should be written on your permit to work that there will be auxiliary live supplies, and that you must test according before performing any work...assuming you have a permit system wherever your working of course . Stick a 'auxiliary circuits isolated elsewhere' sticker on the front.....job sorted

 

[Knobhead]

It should be written on your permit to work that there will be auxiliary live supplies, and that you must test according before performing any work...assuming you have a permit system wherever your working of course . Stick a 'auxiliary circuits isolated elsewhere' sticker on the front.....job sorted

Who is going to issue that permit? Often there will only be one electrical person on a plant, he should be conversant with the systems in use.
If a person needs a note on the permit warning of multiple control systems do you think that person should be working on the system?

All equipment on our plants came under the jurisdiction of a process supervisor. He would make out a permit to me handing over an individual machine or a section to me as shift engineer giving me jurisdiction.
I would then involve other trades as isolation may not be just electrical.
Electric.
Hydraulic.
Pneumatic.
Steam.
Noxious gasses.
Radiation.
Explosion.
Kinetic energy (often overlooked but a killer non the less).

Then there are the environmental hazards that could endanger others, not just the individual.

By handing the plant over it comes under my jurisdiction as the shift engineer. If the work is say a single motor then I will isolate and lock off locally, for larger systems then isolation will be “as required”. As required is what I deem is required to make the job as safe as possible.
One particular job springs to mind, nothing major, change a thermocouple. 77 individual isolations required.
Any of the other tradesmen on shift could ask me to prove isolation but it was also up to them to ensure their own safety.

Go in to an environment where multiple systems are integrated then much of the onus is on the individual. Stray control voltages are often the least of your problems.

 

[Jamzie]

Suppose it depends which avenue you've gone down Tony. I can only refer to heavy industry and power generation, as that's all I've worked in where permits are concerned. As a SAP on a coal station, I used to isolate, prepare and issue permits for apparatus upto 11kV. If there were any anomalies then these had to be clearly stated on the document and verbally read out. I assumed permits were standard affair in industry.....obvious not! Never done a 77 point isolation for a thermocouple though.

 

[Deleted member 26818]

Another problem, is if the person who would issue a permit, is not aware that a particular machine will have live parts when isolated, how will they know to issue a permit?

 

[netblindpaul]

Spin,
They are not competent to issue a permit, if they are not aware of the risks, full stop.
That so called argument is a non-starter.

 

[TailSpin]

Thanks All

for your comments .
This perticular Panel has main isolator on the front with inverter inside with some other circuits which stay alive when isolator is off , they incude panel lights which is fed from a transformer, and cooling fans.
These things are fed from a second multicore cable.
This could bring in another question is it a duel feed Panel ?
and the panel isolator is the local isolator for the motor .
If this is the case I would need a permit to work.
Just to mention the Isolator before this panel will kill both supplies.
I guess I need to be more intouch with BS EN standards for machinery panels,


Regards
John :thinking:

 

[netblindpaul]

Now that does, sound wrong.
All equipment of all sorts in the one panel, should, really be fed from the same incoming supply.
That is all barring interlocks between machines say.
The lighting should be fed from the incoming side of the main isolator in suitable cable to it's own circuit breaker/isolator.
Who CE marked the panel?

 

[Knobhead]

Suppose it depends which avenue you've gone down Tony. I can only refer to heavy industry and power generation, as that's all I've worked in where permits are concerned. As a SAP on a coal station, I used to isolate, prepare and issue permits for apparatus upto 11kV. If there were any anomalies then these had to be clearly stated on the document and verbally read out. I assumed permits were standard affair in industry.....obvious not! Never done a 77 point isolation for a thermocouple though.

I’m only referring to heavy engineering, it’s all I’ve ever done apart for a short spell as production manager.

The permits I issued as AP/SAP would be in addition to the permit issued by the plant supervisor. He hands the section of the plant to me, I in turn would do the MV isolations/earthing required and issue a permit along with the original permit to the work team.
If the work was purely on the distribution system then the plant permit wouldn’t be required as it wouldn’t be affected.

The 77 points of isolation, it was on a coal plant.

 

[Darkwood]

I've worked in many industries subbing in and the most strict one I found was Allied Colloids (Chemical works Bradford) now known as Ciba and was the scene of one of Europes worst chemical fires... You needed a permit and a working pass for any power tool or anything that could create a spark... ..a simple 30min job always took a morning because of the red tape attached. Lost a work collegue their through a skylight - not expected from a company with strict H&S in place. The rest of the companies I work for don't even know what risk is.... Asian, Polish you name it operating machinery with no guards and can't speak the lingo never mind read the warning on the machinery..... I forgot how many jobs I've walked on shook hands - seen the state of the place and walked out and said good luck!

 

[TailSpin]

Now that does, sound wrong.
All equipment of all sorts in the one panel, should, really be fed from the same incoming supply.
That is all barring interlocks between machines say.
The lighting should be fed from the incoming side of the main isolator in suitable cable to it's own circuit breaker/isolator.
Who CE marked the panel?

Hi Paul
this is the thing the named panel has in affect two supplies the main 3phase supply and a multicore cable also comes in the panel to a row of mcbs. This then feeds a transformer to indicator lamps to show supply on faults ect . Other mcbs fed fans ect.( 230v )
The Main Isolator that feeds this panel kills all supplies.
A local contracting firm built the panel no apparent CE mark on panel.
So is this just a case of clear labels if so is there a BS for this type ? I guess Isolate elsewhere would do or might I find the answer in say BS EN 61439-2:2009 ?

Regards
John :confused5:

 

[netblindpaul]

If it is for a machine try 60204-1.
Ask the manufacturer to come on site with their copy to go through the design with you.
If they don't have the standard, then they should not be building panels for machinery.