25a Appliance on Unfused Spur off 2.5mm ring final with 32a RCBO

[ericmark]

I would have said 25 amp for inrush, although most fixed AC's use inverter drives so there should not be an inrush. I noted most fridge/freezers said do not use an extension lead, this was due to the volt drop on start could cause the motor to stall, yet even with the inverter drive models it still says do not use an extension lead, so the 25 amp could be a throw back from earlier models.

I have also been caught out with AC power requirements in the past, where there are two parts, some one read the label on the bit which goes inside the building and it said around 5 amp, however the bit which went on the roof was 7 kW and we had 6 of them from memory, so we had to pull a very large cable in to supply them, after other items had been installed which were getting in the way.

So is that label for whole unit, or just part of the unit? In the main AC's have dedicated supplies, and often motor rated overloads.

 

[ebee]

Well if it is 9A you could put a 10A fuse in if you want instead of a 13A. I gave some 10A fuses out for folk to put in their UK plugs running 4 gang extensions from an adaptor plug in Oz. After a few months they told me not needed because they still work with the existing 13A in place. I tried to explain that their Oz sockets were rated at 10A therefore no more than a 10A fuse should really be used. I gave up

 

[EFLImpudence]

I gave some 10A fuses out for folk to put in their UK plugs running 4 gang extensions from an adaptor plug in Oz.

That must be some Volt drop.

 

[Adam_151]

I've generally found that AC units quote some funny figures for max current, AFAIK this is generally the absolete max under some very poor conditions, heavily loaded and running at the bottom end of the voltage tolerance (noting that inverter driven units are not simply resistive and will seek to maintain the desired power, so will increase current when the voltage sags).

Digressing a bit

If you design the distribution for a commericial building heated by ASHP and don't realise this, then you might end up with some quite big demand numbers, I normally used the HP ratings of the condensor plant as a starting point, and then you have to figure out what diversity you can then apply on top, which isn't always straight forward, when you have a VRF system, the designer on the mechanical side can apply diversity on the AC side, i.e. the cooling capacities of the inside cassettes is more than the total cooling capacity of the plant, but some systems are designed 1:1, obviously less electrical diversity can be applied to the former than the later, but how much in each case can vary, cooling machine rooms is very different to cooling classrooms...

Back on topic..

Personally in the OPs situation, I'd feed it from a switched fused spur, with a 13A fuse fitted and likely 1.5mm cable assuming a short run, I'd also make sure that if the circuit was on a type AC RCD that it was upgraded to type A. (I normally roll my eyes a little at those who insist on an upgrade when a minor addition has been made to a cirucit, but here, we are adding a sizeable inverter drive to a circuit feeding socket outlets. So quite high up on the list of things which 'could' blind RCDs, and also sockets quite high up on list of things that you want to avoid blinding of RCDs on)

 

[JohnW2]

I've generally found that AC units quote some funny figures for max current, AFAIK this is generally the absolete max under some very poor conditions, heavily loaded and running at the bottom end of the voltage tolerance (noting that inverter driven units are not simply resistive and will seek to maintain the desired power, so will increase current when the voltage sags).

Maybe, but 9A is more than double 4.3A so, if that were the only consideration/reason, one would be talking about voltage 'sagging' to less than half of its usual level !

'Start-up' current is, of course, a different (and valid) consideration, primarily when large motors are involved.

Kind Regards, John

 

[mike42]

Interesting discussion.

It would certainly be quite easy for me to add in a fused connection unit for that particular appliance.

I do wonder what this means in the guide though. If non-fused spurs that are fixed appliances are allowed what is the problem? By the way, the instructions do specify 2.5mm and rubber (well h07rn-f or similar). Maybe that's the reason it wouldn't be allowed? (2.5mm t&e through a wall would likely be just too thin for a 32a mcb/rcbo although splitting hairs its maybe not that bad....although as I said putting in a 13a FCU could easily be done but a worry about the 25a) SO seems like the only fully compliant method would be to run a single radial from the board protected with 25a rcbo)

 

[JohnW2]

.... If non-fused spurs that are fixed appliances are allowed what is the problem?

I personally don't think that there is any problem.

By the way, the instructions do specify 2.5mm and rubber (well h07rn-f or similar). Maybe that's the reason it wouldn't be allowed?

If it has a CCC of at least 20A and a CSA of at least 2.5mm² (1.5mm² if MICC)) it would be 'allowed' (as an unfused spur from a 32A ring), regardless of what insulation it had.

(2.5mm t&e through a wall would likely be just too thin for a 32a mcb/rcbo although splitting hairs its maybe not that bad....

As above, 2.5mm² appears to be allowed for an unfused spur from a 32A ring final (although, not for a 32A radial), provided only that installtion method is such that CCC is at least 20A.

although as I said putting in a 13a FCU could easily be done but a worry about the 25a) SO seems like the only fully compliant method would be to run a single radial from the board protected with 25a rcbo)

I'm really not sure where (the thinking behind) this "25A" comes from.

Kind Regards, John

 

[ebee]

I personally don't think that there is any problem.

If it has a CCC of at least 20A and a CSA of at least 2.5mm² (1.5mm² if MICC)) it would be 'allowed' (as an unfused spur from a 32A ring), regardless of what insulation it had.

As above, 2.5mm² appears to be allowed for an unfused spur from a 32A ring final (although, not for a 32A radial), provided only that installtion method is such that CCC is at least 20A.

I'm really not sure where (the thinking behind) this "25A" comes from.

Kind Regards, John

Could it be that a 25A cct is a standard radial circuit where the manufacturers come from?

That must be some Volt drop.

Yes agreed but I`m unsure of the point you`re making here?

 

[pete01]

Yes agreed but I`m unsure of the point you`re making here?

I think its called a joke

 

[ebee]

I think its called a joke

Oh from 25A to 9A would require a big volt drop, yes I get that huumour. I was slow on the uptake as it is Sunday so not get mee thinking heed on yet

 

[EFLImpudence]

No Ebee; you said:

I gave some 10A fuses out for folk to put in their UK plugs running 4 gang extensions from an adaptor plug in Oz.

 

[pete01]

Oh from 25A to 9A would require a big volt drop, yes I get that huumour. I was slow on the uptake as it is Sunday so not get mee thinking heed on yet

I took the joke being, running a supply from Australia, but I have missed jokes in the past

 

[pete01]

No Ebee; you said:

If you have to explain the joke maybe its rubbish, ha ha

 

[EFLImpudence]

If you have to explain the joke maybe its rubbish, ha ha

That's generally true but...

 

[ebee]

Thanks chaps got it. I am thicker than I thought.

PS they were using their UK plugs/extension in Oz but you already guessed that cos you not as thick as me.

Reminds me a bit of Les Dawson many years ago who told folks his dad had built an electric rocket to go to the moon using just ten bobs worth of scrap metal parts but it would cost him Fifteen Trillion Trillion Trillion £s for the flex