Fear of voltage drop!

[HappyHippyDad]

Its been along day, I've just finished off with looking around a big garden which has all sorts of electrical things going and would appreciate a bit of advice on VD.

Garden is supplied by 2.5mm SWA (buried), at present taking about 1000W from a 20A MCB in the garage CU. The chap wants 2 greenhouse fan heaters installed. The run is about 40m's in total.

Max allowable VD = 11.5
VD (mV/A/m) for 2.5mm = 18
length = 40m

so available power = (max allowable VD x 1000)/length x VD

= 16A (approx) = 3680W

Garden is already taking 1000W so I'm left with 2680W for 2 greenhouse fan heaters.

I have 2 questions:

1. Can anyone see a half decent greenhouse fan heater that is only 1.3kW?
2. Really, Really tired and just cant figure out if VD means the cable will be unsafe or the MCB more likely to trip.... ridiculous question I know but I've had a glass of port (yeah I'm ready for the jip :rolleyes2, I'm tired and I just want to figure it out. Quote doesn't even need to be done for a week!

 

[Paultrim123321]

Volt drop means....volt drop! 230,229,228,227,226 where does it stop? depends how far you want to go.
Only the man with BGB and a calculator knows

 

[plugsandsparks]

You have 20A regardless of VD, Vaguely recall heater being quite small, like less than 500W, depends i suppose if its for frost or simulating the tropics.

For this application wouldn't worry too much you probably have shed loads of volts anyway

 

[dave274]

I wouldnt be putting anything else on it, dig it up and replace it. The circuit needs to conform before you add to it and that circuit doesnt.

 

[Brightspark2]

What is drawing 1000W at the moment?...


If you have too high a volt then equipment may not work or will not work efficiently...

 

[telectrix]

stick 'em in, switch on, measure the VD. if it's under 220V at point of utilisation, then start worrying.

 

[VoltzElectrical]

I wouldnt be putting anything else on it, dig it up and replace it. The circuit needs to conform before you add to it and that circuit doesnt.

what part of it doesn't comply and why?

 

[dave274]

Sorry I didnt work it out I just read the 11.5 and the 18 then put 2 & 2 together and got 5.

 

[Guitarist]

What is your voltage to begin with? The main concern is that equipment will not work correctly if the voltage drops too low, but I often test premises with upwards of 245v to start with.

 

[HappyHippyDad]

stick 'em in, switch on, measure the VD. if it's under 220V at point of utilisation, then start worrying.

You've had a beer! :biggrin:

I'm going to wait for a sensible reply!!!

Route is 30m at present, I will have to add 10m SWA and get it all nicely arranged in both greenhouses. I am not going to 'stick em in'!!!

 

[telectrix]

over engineering, over thinking, over spending.

 

[plugsandsparks]

Sounds arse about --- to me though, what size heaters does he need for the plants ?

80W or 8000W, once you have sorted that bit rest follows

 

[HappyHippyDad]

What is your voltage to begin with? The main concern is that equipment will not work correctly if the voltage drops too low, but I often test premises with upwards of 245v to start with.

Even if it measures 245v should I not be basing it on 230v?

 

[HappyHippyDad]

Sounds arse about --- to me though, what size heaters does he need for the plants ?

80W or 8000W, once you have sorted that bit rest follows

True... I asked him what size, but he hadn't bought them yet. The little bit of research I did this evening showed me that they are usually around 1.5 - 2.8kW!!

 

[Guitarist]

Even if it measures 245v should I not be basing it on 230v?

Absolutely, because we all know that the electricity distributors are going to invest billions of pounds making sure that all households get 230v real soon....

 

[plugsandsparks]

True... I asked him what size, but he hadn't bought them yet. The little bit of research I did this evening showed me that they are usually around 1.5 - 2.8kW!!

http://www.amazon.co.uk/Hylite-Elec...376341961&sr=8-15&keywords=greenhouse+heaters

Seen them before like this. These low watt ones keep frost at bay, the bigger ones try and maintain a climate, a bit like keeping tropical fish i suppose.

If he wants a really big one - going to be spinning the meter a tad..

 

[plugsandsparks]

Absolutely, because we all know that the electricity distributors are going to invest billions of pounds making sure that all households get 230v real soon....

Well all i have seen in last 5 years is volts going up and up, now regularly seeing 250V. Its bizarre, anyway its only a heater, not like it wont work, just takes longer to heat the greenhouse

 

[Brightspark2]

So what is drawing 1000W at the moment?...

What I'm getting at is diversity, are these loads all going to be on at the same time?...

 

[HappyHippyDad]

Hylite 4Ft Green Electric Tubular Greenhouse Heater - 180W: Amazon.co.uk: Garden & Outdoors

Seen them before like this. These low watt ones keep frost at bay, the bigger ones try and maintain a climate, a bit like keeping tropical fish i suppose.

If he wants a really big one - going to be spinning the meter a tad..

Thanks Plugs, I saw the lower watt tubular ones but he specifically said 'fan'!

So what is drawing 1000W at the moment?...

What I'm getting at is diversity, are these loads all going to be on at the same time?...

Cheers Brightspark, did think about diversity but the 1000w would probably be on at the same time.. they consist of about 5 lights on sensors as you walk up the garden and 3 pumps which were all on when I was there.

 

[Richard Burns]

Voltage drop will mean that things like heaters will run less hot and lights will be a bit dim.
remember that section 525 says that if the manufacturer says it will work at lower levels of voltage then it is OK.
or the voltage must not impair the safe functioning of the equipment.
Then says the limits.
The MCB will not trip, the circuit will not be unsafe. Though the accessories may be.
Electronic equipment that may need the full voltage might fail.

If you are feeding a supply to the fan heaters can you up the csa of that part so that you have more leeway?
Just googling this heater for instance has a 1kW energy saving mode, like bathroom fan heaters. Could be a thought.
Have you tried splitting down the VD if the circuit splits up or is it all at the end, this could give you more potential!