Car Chargers Chargers

[RyanM]

Hi Guys,

At work, we have had 8 car chargers installed by contractors - they've been and gone, but I was wondering about the earthing of them. (I'm not involved in contractors, so cannot ask them).

What they have done is:
MCB - RCD - Isolator - ran the cables outside on cable tray - then burried the cable under ground - then up through the stand, in to the charger.

- SWA is earthed/made off both ends, and the earth cable has been used.

- First charger is approx 2m from the building, the 8th approx 16m away from the building.

Is this a case of you can take the earth (from the DB), or are you supposed to use an earth spike at each charger? The charging stands are metal, and don't seem to be earthed with a wire, but then again, they are buried in to the earth, approx 2ft deep. Do these need bonding with the earth from the SWA?

I've never understood about exporting earths, hence the question.




Thanks

 

[ericmark]

There are special rules for car chargers. It seems that domestic is different from commercial, and it also depends on the voltage used some have isolation transformers others do not. In the main they are the same as a supply to a caravan, or boat, in that PME (TN-C-S) is not permitted, except for domestic. But since you have no idea how connected in the stand rather pointless worrying about it.

 

[bernardgreen]

Personally I would prefer a charger for a car to have a local TT earthing arrangement and not an Earth exported from the house or company building.

I would prefer the potential on the body of the car to be the same as the potential of the ground that it and I are standing on. And not to be the potential of an exported Earth that was derived from the incoming Neutral of the mains supply to the building.

If the Earth in the building is derived from the Neutral then it should not be connected to the ground rod forming the Earth for the charger to prevent current flowing from Neutral to Ground . This current does not pass through the RCD and hence has no current limiting protection other than the impedance of the ground rod.

 

[ericmark]

When working on a gas installation where there were 100's of earth rods, the supply had a huge resistor in the earth so if the supply earth was not at the same voltage as the plant earth there was a limit to the current as a result. Resistor was about 5 foot square in size.

In the narrow boats isolating transformers is the best method with no earth connection. However also a diode link is used so there can be a 3 volt difference between the two earth systems. I am personally not keen on using diodes, but it is an accepted method.

When I came to connect a narrow boat we used a Class II battery charger as the isolator. Shore power only fed the battery charger no shore earth connection.

So most electric vehicles today have the charger built into the vehicle, where years ago the charger was static and the vehicle had a DC connection to charger. Where a charge point is installed for a single vehicle we will know from the vehicle specifications if the charger needs an earth. However when anything could be plugged in even if the car does not need an earth, an earth still needs to be provided.

So at home it is possible there is no earth connection to the car, but at a public charge point it would clearly need that earth unless like with a bathroom shaver point there is an isolating transformer.

So back to what I said before, without knowing if dedicated to one type of car, one can't really answer the question. When I installed chargers for fork lifts there was no earth to forklift, same with milk float there was no earth connected to milk float, with a scissor lift however there was an earth connection as charger built into scissor lift, but that earth only went to the charger, it did not connect to the body of the scissor lift. With both wheel chair and mobility scooter no earth connection only 24 volt DC between charger and vehicle.

With a caravan or boat you have multi points of use, with a car it is a single point the charger very like the single point with a shaver, so there may be no earth connection to the body of the car.

 

[EFLImpudence]

If the Earth in the building is derived from the Neutral then it should not be connected to the ground rod forming the Earth for the charger to prevent current flowing from Neutral to Ground . This current does not pass through the RCD and hence has no current limiting protection other than the impedance of the ground rod.

If I have read correctly, would the RCD not open?

 

[bernardgreen]

If I have read correctly, would the RCD not open?

No as the current from neutral to rod does not go through the RCD sense coil

 

[RF Lighting]

So much irrational fear of suppliers earth.

OP I'm sure the contractors knew what they we're doing and there is no issue with exporting the supply earth.

 

[bernardgreen]

So much irrational fear of suppliers earth.

Irrational that at hill top site ( wireless comms sites ) with very low impedence ground rod systems any connection of the supply earth to the equipment earth was banned. I recall a site where the supply earth and equipment earths ( ground rods ) were connected and a raised potential on the supply earth caused damage due to high currents flowing through the earthing system.

 

[RF Lighting]

What's that got to do with a car charger?

 

[EFLImpudence]

No as the current from neutral to rod does not go through the RCD sense coil

View attachment 98153

Ah. I see - so


1. What is the objection to that situation?
2. What is the difference between that and main bonding in a large building?
3. Why is the rod not considered as bonding the ground?
4. Is it an argument against TT ing the chargers?

 

[bernardgreen]

What's that got to do with a car charger?

It makes the point that connecting a Neutral derived "earth" to a low impedance local earth can and does create a signficant risk of high current flowing through the earthing system.

If the installer of the car chargeer provides a low impedance "earth" to local ground and then exports the "earth" then reality the Neutral of the supply has been connected to ground. This can then high currents flowing through the earthing system. Very unlikely that the impedance of the charger's ground rod will be low enough for the currents to be high enough to cause any damage. . The risk is small but there have been several instances of fires caused by earth and/or bonding cables overheating when the Neutral has been faulty or damaged ( metal theft ) and the local ground was via a metallic water supply pipe.

 

[333rocky333]

I've never understood about exporting earths, hence the question.


Thanks

Same here, not charger related but.
We do lots of repairs in pubs and sumermarkets, where theres often lamposts and patio heaters up to 100 metres away sometimes, they seem to always use the supply earth mainly via swa, I note Lucy do cutouts where the earth is isolated but most of the ones ive seen fitted have a gland plate and the swa connected both ends.
Am i missing something too

 

[bernardgreen]

4. Is it an argument against TT ing the chargers?

I see it as a reason to TT the chargers with SWA of the supply cable connected to the supply "earth" but isolated from the casing and earth of the TT charger.

3. Why is the rod not considered as bonding the ground?

Mainly because the ground is too large to bond, the currents that could flow could be very high, which may be the reason why 10mm ² conductor is specified for the main bonding of water pipes.

 

[bernardgreen]

Crews had been called to reports of a small kitchen fire, but when they arrived found a string of small fires in a row of six terraced houses. Firefighters quickly rescued the occupants from all the houses, including two people from upstairs bedrooms using ladders. As the film shows, only seconds later an explosion tore through the row of homes.

Around 30 people were evacuated, two houses were partly demolished and four further houses suffered extensive fire and blast damage. One firefighter was taken to hospital with minor cuts.

Investigations revealed that the blast was caused after a piece of cable was cut from an overhead line. This affected the earthing of the electrical network in the area and resulted in some unusual electrical activity, which affected some of the gas pipes within the properties. This resulted in the fires and explosion.

Full article here http://www.examiner.co.uk/news/west-yorkshire-news/amazing-footage-house-explosion-fire-4971943

The ground rod in these houses was the water or gas pipes and the fires were started by bonding cables melting and igniting items. The piece of cable removed was the Neutral

This is one of the instances that made the news, contacts in the Fire service tell me that many similar instances occur but do not get reported in the media.

 

[ericmark]

There should be an isolating bit of pipe which stops current using the gas pipe as an earth. Clearly in this case there was a problem with the gas installation and the gas pipes were not isolated. Also in real terms having one house with the gas pipe earthed could cause a problem, but spread over 6 properties the pipe should have been able to take that load. Yes thieves caused the problem, but there is a little more to it than that. ME in PME stands for multiple earthing it would seem multiple earth rods were not fitted.

I had problems in Suffolk, again it was the lack of multiple earth rods, then the road works hit the neutral/earth the only path back to the transformers earth rod was through a radio amateurs earth pit. The 4mm² earth cable to his shack was not man enough to take the imbalance of a whole street. Result was the cable melted. Worst was he could see it happening, but even with main isolator off, it made no never mind, no switch on the earth. Had there been multiple earth rods then no single rod would have taken all the load, and shared between many rods they would have held.

PME was not the problem, it was poor installation of PME which caused the problem. My parents found they had no earth, I called the DNO and asked what earthing system we were on. They had to send some one to find out, seems not on their records, when he arrived he measured the ELI said it's just within limits and gave them an earth terminal. He did not have a clue as to if there were any local earth rods or not.