EV Discussion thread

JSHarris

The PEN conductor is the incoming combined Protective Earth and Neutral that all homes with a TN-C-S electrical supply have (and that's the majority of UK homes).

What's needed for any charge point installation on a TN-C-S supply (used to be called PME) is PEN fault protection.  There's an insidious fault that occurs on the LV distribution network (outside the premises) where the PEN conductor can be damaged or go open circuit  without any obvious symptoms.  Because the PEN conductor for underground cables is often an outer sheath it's not unusual for that to be damaged without damage to the three line conductors.

When this happens the return current flows via the other two phases and the local three phase supply voltages become unstable.  One consequence of this is that the floating bit of the PEN conductor (the bit on the consumer side of the cable damage) can rise to a dangerously high voltage.  This then causes the protective earth conductor in those homes to rise to the same high voltage.

Not a problem indoors, as homes are an equipotential zone, with all conductive stuff bonded together.  This is a problem for anything outdoors though, like an EV.  The car body sill be connected to the incoming PEN conductor, and the ground around the car will be at or near true earth potential.  A PEN fault then gives rise to an electric shock risk for anyone standing outside who touches the car.

The fix if for either the charge point to include PEN fault protection (many do) or for PEN fault protection to be provided via a separate box in the supply, or by changing the house earthing system from TN-C-S to TT.  The latter was my solution - I didn't bother to use the incoming PEN to provide a protective earth, and instead have this provided via an earth electrode.

michaels

Grumpy_chap said:

Here's something I never thought of.

Got an Electrician round today to quote the installation for the EV charger.  He mentioned that before he can connect the EV charger load, both the incoming fuse and the meter will require uprating by the electricity supplier and the DNO.  I doubt they'll be particularly quick, though the costs might not be too bad as set by the OFGEM (probably).  I hope that can all be done without requiring the main incomer cable being changed.

The DNO did ours (60a to 100a) for free. think it was weeks rather than months.

silvercar

Thanks for the explanation @JSHarris. Tesla chargers don't have built in PEN fault protection, so something needs to be done.

michaels

silvercar said:

Thanks for the explanation @JSHarris. Tesla chargers don't have built in PEN fault protection, so something needs to be done.

If they are not safe it seems odd that they are on sale?

JSHarris

michaels said:

silvercar said:

Thanks for the explanation @JSHarris. Tesla chargers don't have built in PEN fault protection, so something needs to be done.

If they are not safe it seems odd that they are on sale?

They are safe.  For example I could install one here without adding anything and it would be perfectly safe.  The issue is that they aren't specifically designed for the UK market, and the UK has an oddball electrical system where the distribution network can develop a potentially lethal fault.

Lots of reasons as to why we have this system, but it mostly comes back to the same reason we have ring finals (the daftest and most unsafe arrangement possible IMHO).  After WWII we were in deep debt.  We needed to reduce imports and almost all the copper in wiring was imported.  Both the adoption of ring finals and the adoption of PME (now called TN-C-S) reduced copper use.  The use of PME reduced the copper needed for the LV network single phase cables by about a third, so was well worth doing at that time.

JKenH

I was just having a scan through the latest offerings from Tesla and came across this 0 miles M3P, supposedly at an £11k discount. 

https://tesla-info.com/car/GB-LRW3286_c7c1388391cca9b1c731c8de62761bd4

Grumpy_chap

JKenH said:

I was just having a scan through the latest offerings from Tesla and came across this 0 miles M3P, supposedly at an £11k discount. 

https://tesla-info.com/car/GB-LRW3286_c7c1388391cca9b1c731c8de62761bd4

Tesla website does have a handful TM3-P vehicles shown as demo models at £48k down from £59k list.
Not everything they have is listed on the website.

Grumpy_chap

1961Nick said:

I'll be amazed if you don't get delivery before the June quarter end.

I was on cloud 9 yesterday when they called to confirm the collection for 9 am this Friday, 23rd.

A bit less happy when they called back to rearrange to 4 pm next Friday, 30th.  That is "by the skin of the teeth" June...

Martyn1981

Grumpy_chap said:

1961Nick said:

I'll be amazed if you don't get delivery before the June quarter end.

I was on cloud 9 yesterday when they called to confirm the collection for 9 am this Friday, 23rd.

A bit less happy when they called back to rearrange to 4 pm next Friday, 30th.  That is "by the skin of the teeth" June...

That was so funny, I was L'ingOL, so close, so close. I think I may be living vicariously through you, and getting quite excited. 

You're gonna love the TM3, but I suspect you'd be thrilled with any BEV, such a lovely driving experience, even for ex-petrolheads like me.

1961Nick

JKenH said:

I was just having a scan through the latest offerings from Tesla and came across this 0 miles M3P, supposedly at an £11k discount. 

https://tesla-info.com/car/GB-LRW3286_c7c1388391cca9b1c731c8de62761bd4

The warranty was activated on 15th March so it does look as if it's been a demonstrator. If so, it's likely to have done a few miles - although sometimes this can be reset back to zero to remove delivery miles.