Electrical separation (complicated)

[lloydy304]

Hi all,

Hoping for a little advice. I work in the Asbestos industry and we manufacture mobile decontamination units we follow the HSE 247 that states all units must comply with BS7671.

We have had a heads up that new regulations may adopt the use of electrical separation (assuming the use of isolation transformer) inside of our units and removing the need for an earth electrode to be installed at the unit. The worry is that old buildings supplying the unit may have a missing earth or a earth with potential that could transport to our chassis/earthed equipment.

Statement attached.

So how I see it is that the condition of an electrical supply from any buildings or site generators should not be the responsibility of the manufacturers and should be part of the initial site survey. In my opinion the running cable is the greatest potential risk as it can be exposed to heavy machinery, electrical separation inside of the mobile unit will not remove this risk. Running a cable with no earth could be a greater risk if the live conductor was exposed, for example steel wire armored cable has the added effect of causing a more likely short when damaged by using the protective earthed shielding to return the potential and trip the breakers. The risk from using a cable that has no earth connection would still pose a risk to operatives on the site if the cable did not have an earth wire.

At present If a fault occurred inside of the decontamination unit and no earth was present in the supply cable and the chassis was sitting with a dangerous potential, the RCD integral to the unit would operate in the event of an electric shock with a good chance the chassis corner steadies would be a better loop than the person touching it.

A cheaper option would be to have all cables that supply DCU's from buildings to have an inline RCD at the point of the plug outlet on the building and a fixed polarity loop tester installed near the inlet on the DCU that can verify if an earth is present in the system and where no earth is present an earth electrode should be installed at the DCU. This would cheaply allow all legacy units to be converted for greater safety.

Is there something I am missing as this all sounds like a way for contractors to avoid initial verification and push the cost to the manufacturers?

General specifications are:
230v 16A Commando inlet
RCD Protection on all circuits internal

 

[UNG]

Hi all,

Hoping for a little advice. I work in the Asbestos industry and we manufacture mobile decontamination units we follow the HSE 247 that states all units must comply with BS7671.

We have had a heads up that new regulations may adopt the use of electrical separation (assuming the use of isolation transformer) inside of our units and removing the need for an earth electrode to be installed at the unit.

To which new regulations are you referring

The worry is that old buildings supplying the unit may have a missing earth or a earth with potential that could transport to our chassis/earthed equipment.

Are you familar with the regs sec 413 and 418

So how I see it is that the condition of an electrical supply from any buildings or site generators should not be the responsibility of the manufacturers and should be part of the initial site survey. In my opinion the running cable is the greatest potential risk as it can be exposed to heavy machinery, electrical separation inside of the mobile unit will not remove this risk. Running a cable with no earth could be a greater risk if the live conductor was exposed, for example steel wire armored cable has the added effect of causing a more likely short when damaged by using the protective earthed shielding to return the potential and trip the breakers. The risk from using a cable that has no earth connection would still pose a risk to operatives on the site if the cable did not have an earth wire.

If you are producing a unit that is isolated from the supply by the use of an isolating transformer then some of the problem is eliminated, the problem as I see it is where the ioslating transformer is placed although once the supply within the DCU is not referenced to the supply earth then the risk of shock is lessened

At present If a fault occurred inside of the decontamination unit and no earth was present in the supply cable and the chassis was sitting with a dangerous potential, the RCD integral to the unit would operate in the event of an electric shock with a good chance the chassis corner steadies would be a better loop than the person touching it.

A cheaper option would be to have all cables that supply DCU's from buildings to have an inline RCD at the point of the plug outlet on the building and a fixed polarity loop tester installed near the inlet on the DCU that can verify if an earth is present in the system and where no earth is present an earth electrode should be installed at the DCU. This would cheaply allow all legacy units to be converted for greater safety.

I think you are not understanding the use of isolating transformers when the supply has no earth reference there is no circuit to earth
The use of and reliance on RCD's for fault protection in the DCU would require regular checks and maintainance to ensure they are operating within the stipulated limits

Is there something I am missing as this all sounds like a way for contractors to avoid initial verification and push the cost to the manufacturers?

General specifications are:
230v 16A Commando inlet
RCD Protection on all circuits internal

While there will be cost with regards to the isolation tranformer this is not that great in the grand scheme of things IMO and I can see some benefits when it comes to connecting to unknown supplies