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Posted By Martin Taylor
I am sure I should know this but is there an EN standard that decribes when electrical control panels should be fitted with door interlock isolators and when this is not required.
I feel that ALL electrical control panels should be door interlocked isolated but have just been delivered of a system where this is not the case and would like to make a challenge to their CE mark (if somebody can point me in the direction of the appropriate standard).
thanks in advance to anybody who can help
Martin Taylor
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Posted By Jane Blunt Dear Martin Standards come at several levels, from generic to those specific to certain types of equipment. There is a generic standard BS EN 60204 part 1, Safety of Machinery. Electrical Equipment of machines, specification for general requirements. It is not the only generic standard and it is possible that you specific piece of equipment has a specific standard associated with it. See the BSI page for standards (you can log on and do searches without charge) http://www.bsi-global.com/index.xalterI would not expect all equipment to have interlocked doors, provided that you need some sort of tool in order to be able to gain access to parts at dangerous voltages. The CE declaration may define the standards to which it has been built, if you are lucky. Regards Jane
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Posted By Heather Aston
Martin
I would turn this round and ask the manufacturer to justify on what grounds they have not interlocked the control panel. As the previous poster said - it should really be stated in the Technical File, or possibly on the declaration of conformity - they did supply these documents didn't they?
Heather
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Posted By Martin Taylor
thanks to Jane and Heather for your responses.
I think I will have a bit of a fight with the supplier as the work is already done and retrofitting a unit will be difficult. Hence I could do with a meaty chunk of regs to throw at them.
Another way to look at this is does any designers out there have principles to decide whether to use a door interlock isolator or not - when is it acceptable not to.
Heather last point is good too - the panel is fitted with what I would describe as a standard Rittal key - you know the type - large chunky key with T bar on the end - the type that anybody can get open with a screwdriver - again in my book this doesn't count as a secure lock and fixed guard but what do others think?
ta everybody
Martin
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Posted By Heather Aston
Martin
I would expect an electrical control panel which gives access to live connectors to be locked in such a way that it requires a key. I've seen the T-key arrangement on many older machines, but would not be happy about it on new equipment.
Bit late for you now but we've had this problem before and now do not pay the supplier in full until the machine has been fully "signed off" under our internal plant acceptance scheme. I have had suppliers (particularly from Italy and Germany) kick up quite a fuss and assure me they've supplied their machinery (in what I consider to be an unsafe state) all round Europe and never had a problem. My response is "well you're not supplying it like that here". It has usually lead to mods being made as we require!
Oddly enough I have not had much problem with UK manufacturers - they seem to be willing to work with us to solve any issues during the specification stage.
The interlocking argument - when should you do it - is to be honest a matter for risk assessment. If you are likely to require regular access into an area where there are dangerous moving parts (either as part of the normal process or to fix jams, change tools etc) then instead of fitting a fixed guard you should have an interlocked door in a fixed guard. The interlock should not be able to be easily defeated by jamming in the switch with blu-tack (as I have seen on many machines of European manufacture)
Heather
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Posted By Alistair Reid
My experience of door interlocked isolators on control panels is that they create more potential for serious accidents than they prevent. Live working is a necessary evil for many reasons and to facilitate this the link bar between the isolator and the handle is removed and rarely refitted on completion. This then leads to a false sense of security when the operator 'isolates' the equipment it has no effect but the handle is in the OFF position.
Please don't tell me this dosn't happen on your site, it is endemic and very rarely spotted because the people that cause the problem are the only personel authorised to access the panels.
If I was purchasing equipment I would not accept any panel that had door interlocked isolators.
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Posted By Jason Gould
The last respondent has a very good point.
When I was unblocking some granulating machines for the umpteenth time and to my horror, I found that the so-called Isolating switch was a waste of time though it looked intact someone had fiddled with it.
Then get told to Isolate from main electrics room and was left a key to access it. What do I find? lots of nails in fuses.
That was a long time ago and the place is gone now.
Funny side of it was when at a new place I was recalling this story to a sparky that was installing one of your big cables for new machinery. He stated how disgusted he was at the notion.
It turns out he was an alcoholic and was drinking on that day. This is a common fact, as we had to wake him at home time in his tool room on many occasions.
All this happened befor I knew anything about H&S and as you can guess normal naive workers will just sit in brew room and whinge amongst ourselves in most circmstances.
Here's me being all condemming when I never even used pushsticks whilst unblocking and subsequently nearly lost the tips of my fingers.
The bliss of dealing with machinery.
Like you are doing, check compliance with relevent regs with supply law etc. But then have a monitoring plan for electrical boxes etc. Let them know you know.
Good luck
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Posted By George Wedgwood
Panel access is still a nightmare for selectors - especially as most of our equipment is now sourced outside the UK and large assemblies often come from different manufacturers. However, a strict system for access couples with good competence levels for staff who may access panels - two lwvels - operations and maintenance. In my experience, operations staff could crack a bank of england safe! So interlocks only serve to frustrate them in their essential role 'to get it going'. The BS standards etc. are useful guides but I find many suppliers have never heard of them and even if they have, won't pay for expertise to implement them. Simple locked panel doors are best, with a 'permit' system to access and inside, fitted polycarbonate panels to separate the 'dangerous' voltage levels from accidental access, works well. Resetting of overloads and fuse access is most popular, so these should be brought outside the screen if possible, otherwise, a notice should state clearly that an 'Authorised person is only alowed to remove the polycarbonate panel - with tools. Resetting of overloads can be easily achieved by allowing small holes in the panel, which have insulated rods fitten to extend the overload button. We have gone over to (over 240V) trapped key interlocks for panel access so that an isolator must be off before access to high energy enclosures - Fortress or Castell are excellent advisers.
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Posted By Heather Aston
I agree with most of the above regarding the interlocking of control panels. My comments on interlocking were meant in a general machinery guarding context (which is how I read Martin's secondary query - though reading it again I can see it's probably not what he was asking).
I would agree that the best way to lock electrical control panels is with a proper key (not a T-key) and, yes I have seen defeated interlocks and agree that they can lead to a false sense of security - thoughsomtimes if they are tied up with string or stuck in with blu-tack it's obvious....... (no I have not seen this recently!)
Heather
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Posted By Robert.J
I thought that the CE mark, generally, meant that an item was fit for intended end use.The panel isolator will isolate the supply! I can understand the frustrations and the pros and cons of having or not having an interlockable isolator.
Did the original customer spec highlight the requirement of one?
Another consideration could be to mount a lockable fuse-switch,switch-fuse or isolator at the incoming side of the panel, you would definately be able to isolate the panel then.
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Posted By Heather Aston
Robert said "I thought that the CE mark, generally, meant that an item was fit for intended end use".
Quite right.
Also, everyone drives at 70 mph on the motorway and no-one ever parks on double yellow lines....
But seriously - you are absolutely correct it should guarantee that the machine confirms to the EHSRs under the Machinery Directive. Experience tells us that quite often it is not worth the metal it's written on, that's why we have an internal company machinery acceptance procedure for all new machinery.
Heather
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Posted By Martin Taylor
thanks to everybody for their input here - the thread isn't giving me the nice simple answer I was looking for - but there never is in this field is there! Anyway the discussion is very interesting and the principle of not using door interlocked isolators because they will be defeated is an interesting one to debate - again given the everyday nature of the T bar type lock on most small electrical control panels
I look forwards to reading further views
regards
Martin
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Posted By Merv Newman
On the question of "proper keys" or "rittal" keys, It is a long time since I read the regulations but I believe either is acceptable. The principal is that dangerous voltages should only be accessible by means of a tool and thus a delberate act rather than idle curiosity.
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Posted By Stuart Nagle
Martin.
Most modern panels are now fitted with a shield, as mentioned above, so when a panel is opened you can cannot physically make contact with live conductors, but re-setting of trips ect is possible.
The Electricity at Work Regulations make reference to working live, which could of course apply to panels in situations where isolation of supply is not reasonably practicable (principally for safety reasons) when isolation of supply to plant may cause a safety hazard in itself or interupt a process so as to be unreasonable in the circumstances (e.g. a mixer with materials that will set solid). In such circumstances a panel may have been specified to meet these requirements!
However, the onus is to work dead unless there are very good reasons for not doing so.
There are a lot of standards in respect of electrical panels and isolators, and probably the most common type of panel has a combined isolation switch and locking mechanism, that means you cannot physically open the panel without first isolating the supply. Panels that you can open without isolating or that do not contain shields are usually very old (already insitu) or are specifically for a purpose as indicated above. If isolation is not possible at the panel, there should be a method of isolating the panel itself fitted into the electrical supply to the panel.
Hope this is of use
Stuart Nagle
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Posted By D. Hilton
Martin,
I think it unlikely that you could challenge the validity of the provision of CE marking to the equipment in question. The manufacturer/supplier would have needed to comply with EHSR 1.5.1 ‘Electricity Supply’
‘Where machinery has an electricity supply it must be designed, constructed and equipped so that all hazards of an electrical nature are or can be prevented’
One method of meeting this requirement is to adhere to the requirements of E.N. 60204 –1. 1998 ‘Safety of Machinery- Electrical Equipment of Machines’ and in relation to electrical disconnection Requirement 5.3 in particular.
A supply-disconnecting device shall be provided for each incoming source of supply to a machine.
The supply disconnecting device shall disconnect (isolate) the electrical equipment of the
machine from the supply when required (e.g. for work on the machine, including the electrical equipment).
The supply-disconnecting device shall be one of the following types:
Switch-disconnector, with or without fuses.
Disconnector, with or without fuses.
Circuit-breaker suitable for isolation.
Plug/socket combination for a machine with a rated current not exceeding 16 A and a
total power rating not exceeding 3 kW;
Plug and socket-outlet or an appliance coupler for a flexible cable supply.
When the supply disconnecting device is one of the first three types (i.e. a
switch-disconnector, a disconnector used in combination with switching devices, or a circuitbreaker), it shall fulfil all of the following requirements:
isolate the electrical equipment from the supply and have one OFF (isolated) and one
ON position only, clearly marked with "0" and "I'.
have an external operating means (e.g. handle). The handle should be BLACK or GREY and be provided with a means permitting it to be locked in the OFF (isolated) position (e.g. by padlocks).
The handle of the supply disconnecting device shall be easily accessible and located
between 0,6 m and 1,9 m above the servicing level. An upper limit of 1,7 m is recommended.
In reply to your question ‘When should a protective interlock be provided?’
Protective interlocking would only be a requirement in the event that a hazardous condition or damage to the equipment or to the work in progress can occur as a result of two or more supply disconnecting devices being provided at the equipment.
In conclusion, there a number of situations whereby it is not desirable to isolate all electrical equipment located within the panel:
Lighting circuits for lighting needed during maintenance or repair.
Plug and socket outlets for the exclusive connection of repair or maintenance tools and
equipment (e.g. test equipment);
Undervoltage protection circuits that are only used for automatic tripping in the event of
supply failure;
Circuits supplying equipment that should normally remain energized for satisfactory
operation (e.g. temperature controlled measuring devices, product (work in progress)
heaters, program storage devices);
Control circuits for interlocking.
‘It is recommended, however, that such circuits be provided with their own disconnecting device’.
Where such a circuit is not disconnected by the supply disconnecting device:
Permanent warning label(s) shall be appropriately placed in proximity to the supply
disconnecting device;
A corresponding statement shall be included in the maintenance manual;
Regards
D. P. Hilton
MIOSH. MIIRSM,
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