EExd box

[omegadave]

Hi

we installed a EExd enclosure on a skid, the inspector now says the isolator is not door interlocked, and says it shoud be.

Our supplier says is is not required for certification, directive apparently states Door should not be opened unless power is isolated elsewhere.

Please can anyone confirm this fact, or point me in right direction for more information.

also, inspector is saying we do not have earth bond strap on door, supplier of box, again says this is not a requirement.

Any thoughts on this one too ?

all help appreciated

 

[ScottyUK]

Per BS EN 60079-14

Potential equalization is required for installations in hazardous areas. For TN, TT and IT systems, all exposed and extraneous conductive parts shall be connected to the equipotential bonding system. The bonding system may include protective conductors, metal conduits, metal cable sheaths, steel wire armouring and metallic parts of structures, but shall not include neutral conductors. Connections shall be secure against self-loosening.

Exposed conductive parts need not be separately connected to the equipotential bonding system if they are firmly secured to and are in metallic contact with structural parts or piping which are connected to the equipotential bonding system. Extraneous conductive parts which are not part of the structure or of the electrical installation need not be connected to the equipotential bonding system, if there is no danger of voltage displacement, for example frames of doors or windows.

So I agree with your inspector: the door should be bonded, just like it should be in a non-hazardous area.

Regarding the door-interlocked isolator, this is one standard means of minimising risk for entry into any electrical enclosure. I don't think it is specifically called out by the hazardous area regs but the HSE would consider it to be 'reasonably practicable' to provide a door interlock unless you can demonstrate that you have other means of providing equivalent levels of safety from the system. That might be in the form of a permit-to-work system and controlled access to the location, requiring use of a tool to gain access to the enclosure, appropriate labelling and so on. The question you need to ask is whether you would be comfortable defending your design in court in front of industry experts. That's the acid test for any designer, but haz area design is particularly unforgiving.

Here's what BS EN 60079-14 says about isolation:

To allow work to be carried out safely, suitable means of isolation (for example isolators, fuses and links) shall be provided for each circuit or group of circuits, to include all circuit conductors including neutral.

Labelling shall be provided immediately adjacent to each means of isolation to permit rapid identification of the circuit or group of circuits thereby controlled.

NOTE There should be effective measures or procedures to prevent the restoration of supply to the apparatus whilst the risk of exposing unprotected live conductors to an explosive gas atmosphere continues.


Note BS EN 60079-14 isn't specific to EEx'd', it's a generic document for hazardous area installations in surface applications. BS EN 60079-0 allows either an interlocked disconnector or use of suitable warning labels requiring isolation elsewhere prior to opening.


You really need to get hold of the standards - it's a complex subject.


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If we learn from our mistakes I'm getting a great education!

 

[omegadave]

Scotty

thanks

I tend to agree with you about the bonding. Isolator, emm, there is a label on front of panel saying isolate before opening.

apart from googling, is there a good site you can recommend for EN 60079 for getting detail

thanks

 

[ScottyUK]

Dare I say BSI's web site?

There's a lot of useful information from the likes of Stahl, Cooper Crouse-Hinds, Victor, Petrel and so on who are in various markets for haz area equipment, but really the standard is what you need. Your employer should be providing you with it as one of the tools for the job, although I know what some employers are like! You could try one of the commercial libraries too - they can get hold of standards. The 60079 series is a big (and therefore expensive) set so pick the bits you need.

If this is a traditional EEx'd' design with a couple of dozen socket screws or bolts holding the cover shut then my opinion is that you would be ok with suitable permanent labels IF your site has appropriate controls on work, e.g. a PTW system etc AND there is a means of securing an isolation elsewhere. By 'permanent label' I mean engraved stainless steel mechanically fixed to the enclosure or similar.


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If we learn from our mistakes I'm getting a great education!