Supply for Glamping pods

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hockley14

DIY
We are considering putting in two glamping pods on our farm.
The main house has a two phase supply (so im told). The house has a annex connected to it and also stables.
The pods will be situated 300 meters from the main consumer unit. Cables would need to be underground.
At the pods we will need to supply lighting and a few sockets for a kettle, toaster 2 ring hob, fridge and hairdryer. (no heating) A klargester sewerage plant will also be present.
We estimate that if everything is running at once we could have a draw of around 4kw.
So my question is simple!!!!!! what size/type SWA would be required. What volt drop would there be etc.
I look forward to anybodies help.
 
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hockley14 said:
We are considering putting in two glamping pods on our farm.
The main house has a two phase supply (so im told). The house has a annex connected to it and also stables.
The pods will be situated 300 meters from the main consumer unit. Cables would need to be underground.
At the pods we will need to supply lighting and a few sockets for a kettle, toaster 2 ring hob, fridge and hairdryer. (no heating) A klargester sewerage plant will also be present.
We estimate that if everything is running at once we could have a draw of around 4kw.
So my question is simple!!!!!! what size/type SWA would be required. What volt drop would there be etc.
I look forward to anybodies help.
Click to expand...
You need to get an Electrician to design and provide a quote for the works required, the design will provide all the answers you require, I feel it would be wrong to provide any other advice without a site visit, don't make the mistake of buying cable. the persons you employ will get all the correct cabling and accessories needed, trying to help by buying stuff from an internet enquiry would be a false economy in my book.
 
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At 300m and 8kw total load you are looking at a serious wedge of cash on the cable. Id strongly suggest getting a spark in to calculate that, as even one size too big is a LOT more money. Also installing 300m of anything is going to be a massive task, you are going to be talking roughly a tonne of weight.

Have you considered the alternative idea of using camping gas for kettle / hob.12v lighting and fridges and 5v usb sockets supplied from a solar and battery setup? No hairdryer though :)
 
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hockley14 said:
The pods will be situated 300 meters from the main consumer unit. Cables would need to be underground.

We estimate that if everything is running at once we could have a draw of around 4kw.
So my question is simple!!!!!! what size/type SWA would be required. What volt drop would there be etc.
I look forward to anybodies help.
Click to expand...

Your question isn't as simple as you think, and one that will be very costly if the answer is wrong, that's a very long cable to have to replace when it turns out to be undersized!

Any answer you get here will only be an estimate and would need the electrician who designs the circuits to confirm the required size. The size of cable will depend on how the circuit(s) are designed, it may be better to install a single circuit, or it may be better to install one for each pod.

At that distance there may be some earthing considerations, again it will be up to the person designing the installation to establish this.

Having said all that, my rough calculations based on my own assessment of the intended load you have described is that something in the region of 95mm conductors may give an acceptable voltage drop for a single circuit to feed both pods.
However I wouldn't install this size cable, I would design this as a parallel feed to reduce costs and reduce the physical size of switchgear required.
 
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A 3OOmtr cable run needs to be designed properly, you are looking at a fairly large csa cable

what’s wrong with a couple tents and a gas stove :D
 
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Is it worth considering running both phases down a cable to a transformer near the pods.
This would need to be properly designed but volt drop would be roughly half and you could use the right transformer taps to ensure correct voltage at point of use.
 
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Definitely worth getting proper design input based on an accurate site survey at this stage as it could save £££.

To expand on James' comments, if your supply is actually 'split-phase' 230/460V, and if both lines can be used with equal design load on each e.g. one pod per line, this configuration saves copper with minimal extra work. A 3-core cable would be needed but only half the conductor size, so the same voltage drop could be achieved with only 3/4 of the amount of copper, compared to single-phase 230V. That's the worst case when completely unbalanced, with 4kW load on one line and nothing on the other. When the load is balanced the drop will be halved even with a cable half the size, so you would save a few % on the electricity bill.

Adding a transformer at the pod end would remove the need for a neutral and allow the use of a 2-core cable one quarter of the size, since all load would be carried at 460V. The saving would have to be offset against the purchase and running cost of the transformer which would need calculating and might not be economic.
 
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hockley14 said:
yes certainly can. The site is in the middle of a field hence 300mts away. Got overhead power line near but not going to be able to tap into them!!
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Near to where the pods are going to be?

As others have said you can't tap in to them, but the DNO can and that may be cheaper than a correctly sized cable and have the advantage of not having any volt drop or any issues with earthing due to the circuit length.
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James said:
Is it worth considering running both phases down a cable to a transformer near the pods.
This would need to be properly designed but volt drop would be roughly half and you could use the right transformer taps to ensure correct voltage at point of use.
Click to expand...

I looked at this option a few months ago for a 3 phase supply over a similar distance, the transformer option was prohibitively expensive when the ongoing maintainence cost, and downtime should the transformer fail, we're factored in.
 
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I agree that the transformer option might not be useful here, although with a split-phase supply available, the advantage is slightly greater than with 3-phase. Sending the split-phase down the cable is likely to be worthwhile though, as the plant cost and losses are both lower than with single-phase.
 
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An idle moment with on-line tools is saying 50mm and around £3k of cable (BEFORE the cost of installing is factored in) and over 1/2 tonne of it to be wrangled. So you really want to make sure it is the right choice!
 
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pc1966 said:
An idle moment with on-line tools is saying 50mm and around £3k of cable (BEFORE the cost of installing is factored in) and over 1/2 tonne of it to be wrangled. So you really want to make sure it is the right choice!
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What parameters were you putting in to the online tool?
 
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230V single phase, 8kW, 5% drop, 330m, direct in ground method.

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Assuming one sub-main run to both pods and then some splitting arrangement at the end for the pods to share that as needed.
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Of course you don't gamble £3k of cable plus significant installation expenses on an on-line tool's results, you get someone to go through the design properly!
 
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pc1966 said:
230V single phase, 8kW, 5% drop, 330m, direct in ground method.
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Ah OK, that explains the difference from my estimate of 95mm, I was basing it on a 3% (ish) drop and a 40A supply.

I think 40A may still be a bit low without further information on the klargester sewage plant. Plus I think it is fair to assume that there will be water heating of some sort not mentioned by the OP, the presence of the klargester suggests that there will be some sanitary facilities nearby, probably a small building with W/C and washing facilities.
 
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davesparks said:
Ah OK, that explains the difference from my estimate of 95mm, I was basing it on a 3% (ish) drop and a 40A supply.
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I would usually assume 5% is OK for such a sub-main even though there are lights on it as most likely no one load is going to change the supply be much more than 1%.

davesparks said:
I think 40A may still be a bit low without further information on the klargester sewage plant. Plus I think it is fair to assume that there will be water heating of some sort not mentioned by the OP, the presence of the klargester suggests that there will be some sanitary facilities nearby, probably a small building with W/C and washing facilities.
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Very true, also 4kW max load seems small if any heating & cooking together is possible. But I have never "glamped" to know what sort of joys it provides in this way.
 
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davesparks said:
Ah OK, that explains the difference from my estimate of 95mm, I was basing it on a 3% (ish) drop and a 40A supply.

I think 40A may still be a bit low without further information on the klargester sewage plant. Plus I think it is fair to assume that there will be water heating of some sort not mentioned by the OP, the presence of the klargester suggests that there will be some sanitary facilities nearby, probably a small building with W/C and washing facilities.
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No heating and hot water will be via LPG boiler.
They state the klargester at no more than 300w
 
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How far apart are the two glamping pods?

As already covered, you need to be very sure of the total load, and the distances involved, and any plans for the foreseeable future (e.g. any more pods, or any extra facilities like heating), as the installation costs will not be cheap and will cost you a lot more if it is over-specified (or worse and under-specified so has to be replaced).

There are always many way to do something and good engineering is the art of compromise - to meet the goals of safety and functionality at the best price.

With such a cable length you are looking at a lot of metal, and that is expensive, but some of the suggestions still may not be cost-effective in this case. For example, the idea of using 2-core cable from your 480V split supply could save a lot of cable costs, but unless it is well over £1k savings probably won't pay for the transformer. Also transformers have some losses, so trading off the running cost difference may not be so obvious.

You can get aluminium cable but that is rare to see in the UK outside of the electricity supply network and big factories. Aluminium is about 50% higher resistance than copper but much cheaper, so going up a size can still be cheaper in overall cable cost for similar ratings. But it is a pain to work with as usually solid inflexible cores and you need to take special precautions when terminating to avoid galvanic corrosion between aluminium and copper/brass/etc in most equipment. In your case again it looks to be below the point when it would be worth looking at Al cable options (most sparkys would steer clear of that option).

Same for other clever solutions like local power storage to allow a kettle or similar to run at high power for 5-10 minutes with the overall cable load being less for a longer period. While it looks like a neat idea, it probably won't be cost effective and adds a significant reliability question due to the complexity.

So it looks like your best option is going to be just a lot of copper cable. A quick look at the 50mm case would suggest that 2-core cable using the armour for earth is probably just usable with a 40A fuse protecting the feed, but that would very much depend on your supply characteristics. If your supply Ze does not permit that option, it may be most cost-effective to put a time-delay 300mA RCD (or similar) up front to clear cable faults while maintaining selectivity with the galamping circuits on RCBOs, etc., rather than go for 3-core cable to lower R2 as that extra copper core will add something like £4/m to the raw cable cost.
 
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See my #20 in

need to solve voltage drop over long run - https://www.electriciansforums.net/threads/need-to-solve-voltage-drop-over-long-run.187671/#post-1638711

Top 'line diagram' is the conventional long thick cable solution.

Bottom line diagram is local short term 'heavy lifting' provided by battery and inverter. Battery charged by solar pv or thinner long cable or both. Voltage stability and load capacity for glamping provided by inverter.

Or maybe no long cable run at all and have two battery banks - one at the glamping site and the other being charged at the farm which are swapped over say daily. Especial care would have to be taken with the way the batteries are transported back and forth and connected because of the dangers associated with very high energy density batteries - this would not be a preferred practical way ahead so keep it at the back of your mind for now unless the cable run is very expensive. Nota bene - not a task for glampers to do.
 
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Whilst 'Glamping' is a relatively new style of recreational accommodation, caravan sites etc are not. Why not just follow the old style format? As said, you'll probably end up with more.

PS, have you watched Four in a Bed much OP, a lot say 'No, to would you stay here again!'.
 
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davesparks said:
By my rough reckoning parallel cables will be the most cost effective solution, as long as the design is done right.
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I guess it would depend a lot on the details & suppliers. A quick comparison of 2-core SWA in both 25mm and 50mm from Superlec has 660m of 25 coming in at £2,962.08 and 330m of 50 coming in at £2,665.08 so no cost advantage in parallels there. But a whole lot easier to work with!
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marconi said:
Or maybe no long cable run at all and have two battery banks - one at the glamping site and the other being charged at the farm which are swapped over say daily. Especial care would have to be taken with the way the batteries are transported back and forth and connected because of the dangers associated with very high energy density batteries - this would not be a preferred practical way ahead so keep it at the back of your mind for now unless the cable run is very expensive. Nota bene - not a task for glampers to do.
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The battery & inverter option (a makeshift UPS really) has many attractions but I really doubt about the sanity of battery swapping.

Having some solar PV for "free" electric (good from a green PR point of view) would help, but the main attraction and possible justification is you could run a much thinner cable for mains-charging at all times.

While bad from a power loss point of view, it might make economic sense to allow more than 5% drop at peak demand if the charger is OK with that level of AC variation and safe fault-clearing on the cable can be maintained. That suggestion might kick of a whole thread on its own...
 
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Is it worth including the split-phase option in the comparison? Unless one is relying on diversity between the two pods (i.e. the cable design load is less.than 2x the individual pod load) then it should show a saving. One 25mm 3-core on 230/460 will give the same worst-case VD as one 50mm 2-core on 230V single-phase.

Whether the smaller circuit's higher resistance creates or solves OCPD selectivity headaches might depend on whether the pods can be run with one radial, with just the lights fused down, hence allowing lower Ib at the source.
 
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Looking at the 25mm split-phase on 3-core and 50mm single phase on 2-core we have £2,245.32 versus £2,665.08 for the cable costs, so a modest saving of around £420 on basic cables cost. However I have not looked in to the implications for the OCPD arrangements. Quite probably a 3-pole delay RCD could be used for additional cable fault protection in the event fuses, etc, can't meet the disconnection times. Just have to take care about how the self-test works and so which of L1/L2/L3 is left vacant in this case.

Given the quite intermittent aspect of kettles & hair dryers I'm not sure it would be reasonably to assume enough neutral current cancellation to make, say, 16mm split-phase on 3-core a sound choice though, which is a shame as that would save another £500 or so (approaching what a transformer arrangement could offer).

But the diversity on single-phase shared between pods is probably quite reasonable!
 
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Lucien Nunes said:
Is it worth including the split-phase option in the comparison? Unless one is relying on diversity between the two pods (i.e. the cable design load is less.than 2x the individual pod load) then it should show a saving. One 25mm 3-core on 230/460 will give the same worst-case VD as one 50mm 2-core on 230V single-phase.

Whether the smaller circuit's higher resistance creates or solves OCPD selectivity headaches might depend on whether the pods can be run with one radial, with just the lights fused down, hence allowing lower Ib at the source.
Click to expand...

I doubt the one radial per pod with lights fused down will be sensible, the sewage treatment equipment doesn't really want to be on the same circuit as one of the pods in my opinion.

Of course that could have its own circuit, it wouldn't be a very large cable for a 300W appliance even over 330m.
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pc1966 said:
Very true, also 4kW max load seems small if any heating & cooking together is possible. But I have never "glamped" to know what sort of joys it provides in this way.
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I've never 'glamped' personally, but I have looked after power distribution for a couple of VIP campsites at Glastonbury festival a few years ago. I don't think anyone had coined the phrase 'glamping' at that point, but the biggest 'pods' they had their are what I would imagine is being discussed here.

If I remember correctly there were around 12 of the big pods on the second site, each one had a 16A inlet on it and I ran the whole lot from a 200KVA generator. Why 200KVA? Because that's what turned up on the truck despite my having requested something more suited to the actual load. They had lights, underfloor heating, a radio and not much else in them I think.

The first site had over a hundred smaller pods which all got fitted with small 12V batteries (the typical Yuasa burglar alarm style), a maplin solar trickle charger, a bit of led tape and a car cigarette lighter socket with USB adaptor.
 
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davesparks said:
I doubt the one radial per pod with lights fused down will be sensible, the sewage treatment equipment doesn't really want to be on the same circuit as one of the pods in my opinion.

Of course that could have its own circuit, it wouldn't be a very large cable for a 300W appliance even over 330m.
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I've never 'glamped' personally, but I have looked after power distribution for a couple of VIP campsites at Glastonbury festival a few years ago. I don't think anyone had coined the phrase 'glamping' at that point, but the biggest 'pods' they had their are what I would imagine is being discussed here.

If I remember correctly there were around 12 of the big pods on the second site, each one had a 16A inlet on it and I ran the whole lot from a 200KVA generator. Why 200KVA? Because that's what turned up on the truck despite my having requested something more suited to the actual load. They had lights, underfloor heating, a radio and not much else in them I think.

The first site had over a hundred smaller pods which all got fitted with small 12V batteries (the typical Yuasa burglar alarm style), a maplin solar trickle charger, a bit of led tape and a car cigarette lighter socket with USB adaptor.
Click to expand...

Dave, why would you not put the sewage plant on the same circuit as one of the pods? It's only a small load. Just interested.
 
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I would assume that the sub-main feed would be designed to be reliable and at the end you would have a board with separate circuits for each pod and with the sewage plant on a dedicated circuit!
 
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DPG said:
Dave, why would you not put the sewage plant on the same circuit as one of the pods? It's only a small load. Just interested.
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If the pod which supplies the sewage plant was to trip out and go unnoticed, maybe because it is unoccupied for a couple of days, then the people in the other pod would continue to use the facilities.
If that happens then it won't hit the fan, but it will probably backup and cause a rather unpleasant mess.
 
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hockley14

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