Isolation for ac units

[freezy]

Morning all,

Does anybody know where we stand with the ever changing electrical regulations. Most ac engineers wire all interconnecting and control cables on an installation.....is this really okay?

Also should isolation for a wall mounted unit be below or above the ceiling? and where does that leave us with cassettes and condensate pumps which are wired directly into a unit? as the main part of the unit can be reached from within a room.

[Electrocoolman]

Hi Freezy,
If you're competent, then wiring into an Isolating switch should pose no problem under any regs including part P, especially if a sparks has put in the circuit up to the isolator; you would have to have specified what the circuit requirements are, so you should know what size cable to use, but if for example its a single split wall mount then the unit will probably have an mains cable attached already.

If I'm wiring a large outdoor unit I use 'Tri-rated' control panel cable run in flexible conduit between the isolator and the unit. Its easier if you fit 'ferrules' to each end - these keep the strands together and gives the terminal screws something to clamp onto. You can keep cable costs down by just using Black and clearly identifying each cable end (but please use Green/Yellow for the Earth).

The interconnect wiring needs to be sized according to the 'power flow'.....eg if mains power is supplied to indoor unit then interconnect is carrying power to outdoor, and needs to be capable of carrying the current,....but if mains power is supplied to outdoor unit, then cable can be lighter as its only supplying the fan and electronic pcb in the indoor unit (and possibly a drain pump). In this latter case check to see if supply to indoor unit is fused in the outdoor unit to protect the lighter gauge cable.

Have a look at my recent entry under 'cable sizes' in the electrical section and note about fitting fuses to outdoor units.
Don't forget to earth everything properly and ONLY ever use Green/Yellow for this purpose.
For the interconnect, you can get multicore flex 'control cable' with one G/Y core and all others in black with ident numbers. This saves going against the standard colour convention .....ie using blue as a non-neutral, but 4 or 5 core '3 phase' flex might be cheaper and more readily available.

With a single split, with power supplied to the indoor unit, I tend to fit a DP 20A rocker switch or a 13A switch/fuse spur (depending on supply source) up near the ceiling or alongside any trunking...discrete but obvious for future servicing. You can also fit a separate switch/fuse unit for a drainage pump so that this can be correctly fused at a lower rating.

I think the regs state that any isolator should be obvious, ie. not hidden away in the ceiling void.

Most ceiling cassettes are 'power to outdoor unit' so any isolator should be at the outdoor unit.

Needless to say its down to the engineer to isolate the power before working on any equipment (hence the reasoning that any isolator should not be hidden away)

Hope this helps.....regards Adrian

[freezy]

thanks adrian

I really mean isolation of an indoor wall mount, when power has already been supplied to the outdoor unit.

when you say not hidden away...... would it be okay if the ceiling is made of tiles that can be lifted out easily?
Is the isolator just for maintenance purposes or should it be accessible in an emergency ie. fire?

The problem is that customers like to see a nice ac unit, not trunking and switches if they are uneccesary.

[timh1970]

With a single split, with power supplied to the indoor unit, I tend to fit a DP 20A rocker switch or a 13A switch/fuse spur (depending on supply source) up near the ceiling or alongside any trunking...discrete but obvious for future servicing. You can also fit a separate switch/fuse unit for a drainage pump so that this can be correctly fused at a lower rating.


Isolation of the equipment should be provided at both the indoor and outdoor location. This is achieved by cabling 2 isolators in parallel in the supply cable. The last isolator is fitted next to the unit that draws the initial power (In small splits usually the indoor unit).

The reason for this is so that the engineer can isolate it where he is working on it. This prevents other personnel from turning the supply on inside when somebody is working on equipment outside and vice versa.

This is in 16th Edition somewhere but I cannot remember where exactly.

[Electrocoolman]

Hi Freezy and TimH...with power supplied to the outside then there should be a Rotary type Isolator, or equivalent....these can be "locked off" by your own padlock so as Tim rightly mentions, nobody else can switch it back on. I would agree with you Tim that there should be one of these on each outdoor unit especially on a site with multiple units. When power is from the inside unit then don't forget to provide isolation for the reversing signal and other signals to ensure total isolation.
In a domestic installation then (in my opinion) only one isolator is necessary at the source of the power into the installation, and it can be a plug/socket (see regs below)

I don't think that the isolator has to be present for fire purposes...its intended for maintenance use.

I know what you mean by an aesthetic installation, and I suppose you could put the isolator up in the ceiling with a discrete label on the side of the indoor unit directing one to the isolator. This would equate to an ' isolate elswhere ' label that appears on some equipment. The isolator would also need labelling.

Have been looking at the guide to the 16th regs...

"SWITCHING OFF FOR MECHANICAL MAINTENANCE
A means of switching off for mechanical maintenance is required where maintenance may involve a risk of burns and/or injury from mechanical movement.

Each device for switching off must:
i) be capable of switching full load current
ii) be suitably located in a readily accessible position
iii) be identified with a permanent label unless its purpose is obvious
iv) have either an externally visible contact gap or a cearly and reliably indicated OFF position. An indicating light should not be relied upon
v) be selected and installed to prevent unintentional reclosure, such as might be caused by mechanical shock or vibration."

"Every motor circuit should be provided with a readily accessible device to switch off the motor and all associated equipment including any automatic circuit breaker"
"Except where the switch is continuously under the control of the person carrying out the mechanical maintenance, provision shall be made to enable precautions to be taken to stop any equipment being inadvertently re-energised".
"Socket outlets used for switching off for mechanical maintenance shall not have a rating exceeding 16A."

Adrian

[freezy]

Thanks, that's valuble information.

I think I should get myself a copy of the regs;)

[Electrocoolman]

Published by IEE

ON-SITE GUIDE BS7671 : 2001 (2004)

ISBN 0 - 86341 - 374 - 9

Wiring regulations 16th edition Including amendments No 1 : 2002 and No 2 : 2004

Its got a brown cover, spiral bound A5 size and should be available from any Electrical wholesaler, Amazon or IEE.

Adrian

[Makeit go Right]

In a domestic installation then (in my opinion) only one isolator is necessary at the source of the power into the installation, and it can be a plug/socket (see regs below)
Adrian

My understanding of the requirements of the IEE Regs is that you would need the second isolator/switch on a split, even on a domestic install. ie isolate at both Room Unit and Condensing Unit per:


Sub Section 130-06-02
Every fixed electric motor shall be provided with an effective means of switching off, readily accessible, easily operated and so placed as to prevent danger.]


{emphasis added}

[Makeit go Right]

Morning all,
Should isolation for a wall mounted unit be below or above the ceiling? and where does that leave us with cassettes.

Whether to fit the indoor isolator within the ceiling void or surface on the underside of the ceiling tiles, I think you should go for beneath the ceiling tiles.
That way, the isolator is readily accessible in an emergency should there be a need to remove danger from a situation.

Emergency? Well, say a cassette is starting to smoke, or a few flames licking out of the air outlet….the user needs to be able to remove that danger right away by switching it off, right now. (Readily accessible)

Staff, faffing around, asking the tea lady if she knows where the isolator is, or someone says “I think it’s in the ceiling”….someone searching around in the ceiling, lifting 1-9 tiles to look for the isolator, then standing on a chair (if tall enough) to reach up through the smoking ceiling void, up to the slab where the isolator would be fitted.

No, that’s not “readily accessible.”

The switch/switched spur should be fitted where it can be seen. For a cassette that would be to the underside of the ceiling grid. Recess it if you must. And for a wall mount just position it beside the wall unit.