EV SWA Feed Cable Sizing - Oversizing Payback

[Taylorhouse]

Hi All. What are peoples thought on running ev-ultra swa 10mm instead of 6mm on a 15mtr run. I have been asked by the customer as the 10mm has a lower voltage drop per metre. Is there a payback advantage over time. My calculations are the voltage drop difference between 6mm and 10mm is 1.53volts. So that’s about 50 watts for 8hrs a night at 34p kWh is about 14p a night so over the year that’s around £50 a year. With the price difference between the cable only being around £20. That means in 6 months the 10mm cable could of paid for itself. Obviously the figures are all maxed out but is an interesting thought. Installing 10mm takes no more time really. All thought appreciated or are my maths crap.

 

[Chewbacca]

Hi All. What are peoples thought on running ev-ultra swa 10mm instead of 6mm on a 15mtr run. I have been asked by the customer as the 10mm has a lower voltage drop per metre. Is there a payback advantage over time. My calculations are the voltage drop difference between 6mm and 10mm is 1.53volts. So that’s about 50 watts for 8hrs a night at 34p kWh is about 14p a night so over the year that’s around £50 a year. With the price difference between the cable only being around £20. That means in 6 months the 10mm cable could of paid for itself. Obviously the figures are all maxed out but is an interesting thought. Installing 10mm takes no more time really. All thought appreciated or are my maths crap.

Figures sound about right, although charge rate can vary. I would also consider that there's less chance of anything overheating and therefore it will extend the life of the cable. Someone once posted a guide to cable life, what stuck in my head was a cable running at it's max ampage 24/7 could fail after only 5years.

 

[kerching]

There is an online payback calculator somewhere ( maybe something like the copper development council ) we used it years ago,for some BFO 400mm sngle core AWA feeds from a transformer to comms room. Could have used 300mm doubled up, used 400mm doubled up,and the savings were considerable

 

[unphased]

To be honest, I find it astonishing that you even considered a saving against a voltage drop on a cable. I'm not gonna do the maths but personally I wouldn't ever consider the running costs of some electrical equipment in terms of increasing a cable size. You should design a circuit for volt drop of course, but turning that in to a cost saving is pushing things to the realms of bizarre. When you consider the overall price of the EV charger. the cable. parts etc and add your labour on top, there is no 'saving'. The perceived saving is negligible in the extreme. Personally you ought to have used the 6mm2 on being the correct size for the job.

 

[binky]

To be honest, I find it astonishing that you even considered a saving against a voltage drop on a cable. I'm not gonna do the maths but personally I wouldn't ever consider the running costs of some electrical equipment in terms of increasing a cable size. You should design a circuit for volt drop of course, but turning that in to a cost saving is pushing things to the realms of bizarre. When you consider the overall price of the EV charger. the cable. parts etc and add your labour on top, there is no 'saving'. The perceived saving is negligible in the extreme. Personally you ought to have used the 6mm2 on being the correct size for the job.

I've frequently oversized cables on solar jobs, over the 30+ year lifespan of the panels, it adds up. Nothing extreme, just up one size. I've also repaired quite a few systems where the installer has used minimum size cable, and connections have burnt out. Now fair to say, its probably the termination that caused the problem, but it's easier to get a good connection with larger cables sometimes.

 

[Sidewinder]

"Over sizing" cables for energy saving is not unusual on larger commercial jo s, and s creating into domestic.
Once Part 8 comes in. or EN 603645-8 becomes mandatory, then undertaking energy loss calculations for cables will become the norm.

 

[unphased]

Just to clarify, the principle of saving energy has become the forefront of pretty much all areas of engineering. I am all for it. I was just bemused that voltage drop in a cable was being considered as a justification for making a cable larger over a distance of 15 metres! I await the forthcoming Part 8 with interest to see whether voltage drop will be one of the aspects to be considered.

 

[Sharpend]

Sorry to say but this is all smoke and mirrors isn’t it?
At which point do you stop? One size up two sizes up or five sizes up for future proofing?
And are we really going to see ALL participating in this or will it just be the ‘qualified’ brigade?
I often select a cable on a commercial/industrial job the next size up but that’s purely a future proof never an energy saving motive!
And who is going to benefit from this energy saving? You will say the end user but reality tells me that the price of energy will just increase to maintain Profit for the Cats??

 

[unphased]

I agree, Sharpend. I just cannot believe that VD will be one of the techniques employed to save on energy. Like you say, energy prices vary anyway and its always going to go up in price. Its just a non-starter for me, I'm afraid, there is no real saving at all by just increasing a cable in size. I can understand it being considered where massive voltages are involved, but not in domestic situations. Parallel conductors would achieve better returns than bigger ones.
tbh I am not a big fan of the term future proof either. You cannot foresee what the future may hold and with the rate of change it makes it more of a stab in the dark than a proof.

 

[SPECIAL LOCATION]

tbh I am not a big fan of the term future proof either. You cannot foresee what the future may hold

Taking a side step away from the "electrical technical bits" for a minute,
and just pondering the concept of "Future Proof" with regard to domestic dwellings...

In some cases there can be a relatively short timeframe between some peoples occupancy duration..
So future proofing may not always benefit the current occupier....
Unless you are 100% sure you will NOT be moving!!!


Me and Mrs Spec-Loc' (are probably the exception to the rule and), have been living in our first house from way back many years ago when we got married..

But.. just trying to think around my peer group of friends and family etc.....
There are a considerable number who have moved house multiple times!!

So how far into the future, should you consider "Future-Proofing"....
My eldest son is now living in his fourth property...
Eldest daughter in their second home..
Youngest son currently looking to move as changed jobs this month!

One of my wife's best friends from her school days.. is now living in their fifth home..

SO..
The question is, if you are considering "Future-Proofing", How far into the future should you plan your proofing...?
Before someone else will reap the benefits of your future planning.... rather than you??????

Just pondering???

{Straw Poll..... how many on here have never moved house??}

 

[johnb2713]

Were on our third and final house, I'm sure when were gone my eldest boy and his partner will move in here. With that in mind I have planned systems and installations in the house to help with the future eg the solar install and the batteries are installed to a higher spec than if it was just for my remaining years, were doing some building in the garden and using seasoned oak for the frame much more expensive than the usual treated softwoods but it's for the future. Whilst the term future proof can never be taken literally it really means with the future in mind.

 

[Andy™]

I agree, Sharpend. I just cannot believe that VD will be one of the techniques employed to save on energy. Like you say, energy prices vary anyway and its always going to go up in price. Its just a non-starter for me, I'm afraid, there is no real saving at all by just increasing a cable in size

do you still only use halogen lamps? why bother upgrading to LED to save energy, energy prices vary anyway and its always going to go up in price. . Its just a non-starter for me, I'm afraid, there is no real saving at all by just using more efficient lighting

 

[Andy™]

Sorry to say but this is all smoke and mirrors isn’t it?

tbh I've never really bothered to do much calculations as to actual losses cost wise but if the oiginal post is correct then it could be a significant saving. on a shower not so much, but for high loads that are there for hours at a time then yes it would be worth it long term

 

[Sidewinder]

Volt drop is only a part of the calculations.
It is Joule heating in the cable that is ultimately the important value, and volt drop is a part of this Joule heating calculation.
Balancing the lifetime cost of energy lost through Joule heating against the cost of the purchase of that energy against the increased cost of the cable itself is the critical calculation to make and assess.
If the saving in Joule heating is justified against the increased cost of the cable, then it is sensible to increase the cable size.
This will become compulsory for large loads running over prolonged periods, such as EV charging, and it may be required for others such as air or ground source heat pumps.
Along with others, it as has been suggested, difficult to ascertain many loads in domestic situations in most applications.
Apart from some of the "new" loads such as the above.
Perhaps not accurately, but close enough to justify the cable increase against the cost of the Joule heating of the cable by the load.
Yes, it is unclear and not necessarily precise. But part 8 will require this and it is already published.
1. https://knowledge.bsigroup.com/prod...nal-aspects-energy-efficiency/tracked-changes.
2. https://knowledge.bsigroup.com/prod...low-voltage-electrical-installations/standard
3. https://knowledge.bsigroup.com/prod...-prosumer-s-electrical-installations/standard

1. £388
2. £20
3. £198

So it will cost you £388+£20+198= £606 for part 8.

Makes BS 7671 look cheap eh?
Plus there may be more parts to 8 to come!

Don't ask me why there is such a disparity between the cost of the documents, though the only link I could find to part 1 is a tracked changes (TC)
document, which includes the original document marked up with the changes, and the pristine new document. So effectively two documents. Perhaps the reason for the cost increase
Why part 2 is so cheap against part 3 again I have no idea.

Once the scheme providers insist that we have access to Part 8, then we had better hope that cheaper ways of accessing these documents have come along.


Remember, don't shoot the messenger, I don't work for , or represent BSI, Ijust got this information from searching on the open web, anyone can find this by searching.

 

[Sparkless]

udo you still only use halogen lamps? why bother upgrading to LED to save energy, energy prices vary anyway and its always going to go up in price. . Its just a non-starter for me, I'm afraid, there is no real saving at all by just using more efficient lighting

Nonsense. Using more energy-efficient services will result in greater savings as energy prices increase. Simple logic. And the environmental benefits should be considered too.

 

[shaunuk]

I’ll take a 6 month roi any day. Give me the bigger cable I’m always suprised how installers don’t care about the customers costs. In fact I’ve made a business installing batteries for people that have just had heat pumps installed

 

[binky]

I’ll take a 6 month roi any day. Give me the bigger cable I’m always suprised how installers don’t care about the customers costs. In fact I’ve made a business installing batteries for people that have just had heat pumps installed

It's not so much don't care as not been taught to think that way.

Interesting business model.

 

[unphased]

I suppose when the dangers of electricity were first realised, and the first attempts at regulating installations were published, the focus was on the method to make sure it was safe. Unfortunately, BS7671 has lost its way. It has become embroiled in anything and everything. It's sad really because the opportunity to keep it simple and avoid all the baggage enveloping it has long gone. When you attempt to involve energy saving, environment, types of user, and all the other stuff too long to list, it loses its effectiveness. Electricity can be installed safely. That's what the Regulations SHOULD have limited themselves to. Other aspects like energy saving, as one example, are a separate issue entirely from safety. In fact too much dialogue in BS7671 wonders off in to territories it should not ever get involved. The result is an ever expanding wordy document that trys to be all encompassing. In many respects it is almost naive in its approach, trying to pretend it improves safety. Safety is embedded in it but sadly it is lost in an overwhelming conglomeration of unnecessary padding that does not belong. If it focused on safe installation of wires, it would be so much more effective. A simple example is bare conductors. Unsafe. Put insulation around it. Safe. The current approach is to add a thousand words and embroil a hundred factors to that. I would call it being smart arsed. That's the result of trying to be too clever.

 

[Sparkless]

Yep

 

[UNG]

I suppose when the dangers of electricity were first realised, and the first attempts at regulating installations were published, the focus was on the method to make sure it was safe. Unfortunately, BS7671 has lost its way. It has become embroiled in anything and everything. It's sad really because the opportunity to keep it simple and avoid all the baggage enveloping it has long gone. When you attempt to involve energy saving, environment, types of user, and all the other stuff too long to list, it loses its effectiveness. Electricity can be installed safely. That's what the Regulations SHOULD have limited themselves to. Other aspects like energy saving, as one example, are a separate issue entirely from safety. In fact too much dialogue in BS7671 wonders off in to territories it should not ever get involved. The result is an ever expanding wordy document that trys to be all encompassing. In many respects it is almost naive in its approach, trying to pretend it improves safety. Safety is embedded in it but sadly it is lost in an overwhelming conglomeration of unnecessary padding that does not belong. If it focused on safe installation of wires, it would be so much more effective. A simple example is bare conductors. Unsafe. Put insulation around it. Safe. The current approach is to add a thousand words and embroil a hundred factors to that. I would call it being smart arsed. That's the result of trying to be too clever.

Welcome to the world of litigation
The regulations are written in legal speak and have been for around 30 years so the prosecution and the defence can argue points around the prosecutions case with little or no presumption of what is meant or intended