Unswitched Neutral For Airconditioning

[rocketsam15]

Ok..... So.... My main line of work is as an airconditioning engineer although I have taken qualifications in electrical to keep installations safe and proper.

Manufacturers of the kit we install ask for an unswitched neutral between the indoor and outdoor unit of a system. The outdoor unit supplies the indoor unit. As far as I can remember, any piece of current using equipment should be able to be isolated from a nearby isolator. And after shaking my head and rattling it a bit I'm sure the neutral should be switched as it is a line conductor.

But, as our kit uses the neutral to send a signal, a break in the cable causes communication problems. What I propose to do is this........

Run the supply from the outdoor to the indoor unit and terminate all cores to relevant terminals except for the the live which I will send internally on the indoor unit to a SFCU mounted on the side and THEN back to the live terminal.

Does this sound like a reasonable and acceptable solution

Regards

Sam

 

[steptoe]

Ok, Im getting a bit confused with the mixing up of the names,

Neutral is a LIVE conductor, so is LINE, which used to b called PHASE.

Maybe its just me.

 

[rocketsam15]

Ok so yes, neutral being a LIVE conductor should be switched as well as the LINE conductor. Sorry for the confusion of terminology . Didn't rattle my head hard enough

 

[ProDave]

This confused me "But, as our kit uses the neutral to send a signal, a break in the cable causes communication problems"

So what "communication signal" with respect to what reference?

But surely, if the thing is turned OFF by the isolator (even if it only disconnects L) then as the unit is OFF, it can't be communicating? : headbang

So exactly what is getting upset?

 

[rocketsam15]

Ok... So with airconditioning equipment they can use the neutral to pass a 12v dc signal from the outdoor to,indoor unit. If you were to break the neutral and run it through a switching device, i.e. a switched fused connection unit, that is enough to change the resistance in the neutral and play havoc with the signal being sent up it when the switch is turned on and the unit running!!!

Hahaha the little man smacking his head cracked me up . I hope I'm starting to clarify this now

 

[ParkySparky]

I have never seen an aircon fitter put a FCU between indoor an outdoor unit! If it needs working on then they just throw the rotary isolator which is usually mounted on condenser unit outside!!!!

 

[Steve3948]

Also the rotary isolator will have a lock off facility so all good.

 

[SLIPSHOD & SLAPDASH]

I also cant see what the problem is. The isolator adj to the outside unit switches it all off, no need for anything else.

 

[binky]

you could stick label on indoor unit saying isolate at outdoor location - would only be for occasional maintenance. Whilst it preferable to have local point of isolation, it isn't always a feasible idea, but by labelling as appropiate, you are giving a third party the info they need to operate safely.

 

[rocketsam15]

@parkysparky

Well I know what you mean, I have seen this before and used this method myself in the past. But the company I now work for state that they want isolation local to the unit to allow for easy maintenance and safety. So I just have to establish wether it is safe to do it this way. Potentially there could be a fault to neutral which could cause a dangerous situation if somebody isolate via the FCU and only the line is isolated

I also agree with the rest of you chaps, but I have to prove this point to the people above me. Not always easy when "they know best"!!!

To be devils advocate though. If you get called to a job and the condenser is mounted 6 miles at the end of the building through 25 security doors and half way up a cliff, then maintenance or repair and test work can be a b***!

 

[Evans Electric]

I don't quite get it either TBH.   If its an "Isolator"  then its an "Isolator" ...it " Isolates" , once isolated, any signals the designer has decided to send up the neutral instead of a seperate signal cable  will stop ..........reason being ...its isolated. 

But then I'm just a Sparky ..not " one of those above you"   who just alter the regs when they don't suit  them.

Bit like a job I was on once , a college annex,  they wanted the fire alarm, emergency lighting  and dedicated feed to the computer suite to by-passs the main switch to the building .  

We refused to comply , the main switch does what it says on the door ...silly as it sounds ... it turns EVERYTHING off .  We agreed to do it if they put it in writing ....no such request was ever received by us .

 

[kme]

You wouldn`t need to be able to isolate the internal head, whilst the external unit was energised - unless its a multi-head unit, serving several cassettes.....but that doesn`t sound like the scenario you describe.

In my opinion, the internal and external units work together as a single entity - therefore, the requirements of local isolation apply to the whole system - I wouldn`t expect to see a seperate iso. for the internal unit.

In any event - depending on the type of earthing system employed within the building, the neutral may not need to be switched - but even if it doesn`t - once the phase/line/live conductors are disconnected, there aren`t likely to be any "signals" being received by the indoor unit - it hasn`t got power anymore!

 

[Andy™]

I don't quite get it either TBH.   If its an "Isolator"  then its an "Isolator" ...it " Isolates" , once isolated, any signals the designer has decided to send up the neutral instead of a seperate signal cable  will stop ..........reason being ...its isolated. 

But then I'm just a Sparky ..not " one of those above you"   who just alter the regs when they don't suit  them.

Bit like a job I was on once , a college annex,  they wanted the fire alarm, emergency lighting  and dedicated feed to the computer suite to by-passs the main switch to the building .  

We refused to comply , the main switch does what it says on the door ...silly as it sounds ... it turns EVERYTHING off .  We agreed to do it if they put it in writing ....no such request was ever received by us .

you can have more than 1 'installation' in a building, therefore you can have more than 1 'main switch'

 

[Evans Electric]

Yes if there are two supplies Andy,  but one supply = one main switch ...unless they altered the regs .

Not talking domestic here .

 

[Andy™]

Yes if there are two supplies Andy,  but one supply = one main switch ...unless they altered the regs .

Not talking domestic here .

you can have 2 installations even if there us 1 supply