AC Isolation Predicament

[RobFurn]

I work in the Air Con industry. I have a little predicament regarding isolation. Usually you would connect the DB to the external Compressor unit first then connect From the compressor to the internal fan via a control cable. The lockable isolator is positioned next to the external unit, and when your carrying out maintainance you can isolate and lock it off essential if your working on the inside unit. The regs state that the isolator should be positioned as close to the unit being supplied as possible. Or if isolated remotely a means of locking off is necessary. Im fine with all that.
Some small "Home" AC systems are powered from the CU to the internal unit first and then the internal unit is connected to the external unit by the control cable. sometimes you would connect them from the ring off a fused spur and sometimes you would connect them on a separate circuit. Ok anyway my point is if you put and isolator next to the internal unit and carry out maintainance on the external unit then whats to say someone wont switch it on when your working outside i.e. you cant lock it off. My question is should we install a second 2 isolator outside. Another idea would be to put a lockable isolator next to the outside unit, wire from CU to Isolator then from Isolator to Internal unit, then contol cable from internal to external. The beauty about this is you could isolate for maintenance from the external unit and lock it off safe in the knowledge that both internal and external units are off and locked off. With this scenario there would be no isolator next to the internal unit, and probs here? seeing as thought the regs say the isolator should be as close to the unit being supplied. Would apreciate your thoughts. I know in a home you would usually switch it off at the CU regardless but Im trying to satisfy the regs and sometimes all sence goes out the window.

 

[sparkydude]

Hi Rob, In my oppinion i would just add a lockable isolator to the outdoor unit in the control cable, and take the control cores through the switch also as then when its locked off it isolates all forms of supply to the external unit. If you fit MK spurs inside the house to isolate the indoor unit i believe you can remove the fuse and insert a padlock to prevent these from being energised innadvertantly .

Nick

 

[RobFurn]

Nick

Thanks for the reply, good tip re the MK spur. My only concern with fitting 2 isolators is that if you knock the external one off the internal unit is still energised. Im thinking that a 3rd party not knowing could inadventantly think the lot was off and Like I say im just trying to satisfy the regs and be safe at the same time.

 

[sparkydude]

label the external isolator and the internal spur with dymo tape saying

ISOLATE ALL SUPPLIES BEFORE WORKING ON THIS EQUIPMENT.

Your covered then .

Nick

 

[securespark]

If it's DOM, then just lock off the MCB, no?

 

[RobFurn]

If it's DOM, then just lock off the MCB, no?

Thats fine but I have to be whiter than white, as in Jan our NICEIC inspector wants to see some domestic work, were going for a defined scope of the Approved Contractor scheme so Im concerned about the best way to show compliance with regard to "Safe means of Isolation" the regs in my mind is not crystal clear with isolation for mechanical maintainance at the CU. any thoughs or interpretation of the regs that will put my mind at rest?

 

[ericmark]

Normally a FCU is designed so when the fuse carrier is out a small lock can be placed through the carrier to prevent it being pushed back in. Are you aware of this design feature?
I realise 514.1.1 requires where the operator cannot observe the operation of switchgear and controlgear and where this might lead to danger, a suitable indicator shall be fixed in a position visible to the operator. And this could be read as requiring an isolator outside I have never fitted a domestic unit and all commercial units as you say have a local isolator outside.
Eric