Outdoor Socket Advice

JohnW2 · 30 Mar 2021

ericmark said:
I think there is a problem with DC, but what is not clear is the extent of the problem.

Exactly, and it's the grave difficulty I have had in trying to ascertain "the extent of the problem" that I have been moaning about for a long time.

Given that lack of information, I obviously don't know for sure but, as I have implied, I would be pretty surprised (if not amazed) if 6 mA of DC (or anything remotely as low as that) were enough to 'disable' a Type AC RCD.

I think the time may have come at which I have little choice but to do some experiments

Kind Regards, John

Aragorn84 · 30 Mar 2021

JohnW2 said:
Exactly, and it's the grave difficulty I have had in trying to ascertain "the extent of the problem" that I have been moaning about for a long time.

Given that lack of information, I obviously don't know for sure but, as I have implied, I would be pretty surprised (if not amazed) if 6 mA of DC (or anything remotely as low as that) were enough to 'disable' a Type AC RCD.

I think the time may have come at which I have little choice but to do some experiments

Kind Regards, John

Youtube video time?

ericmark · 30 Mar 2021

The John Ward test rig

used 50 and 250 mA so yes we know 50 mA causes a problem, and at 50 mA it tripped at 70 mA and at 250 mA it took 210 mA to trip with that RCD, clearly any other RCD could likely have different tripping currents, however from the two tests it does seem it will trip, but at a higher current.

We have talked before about if the use of a 100 mA RCD is a fail where bonding has not been completed in a bathroom, OK with owner occupied hardly matters, but if potentially dangerous with a rented property hard to say not potentially dangerous with owner occupied property.

So rules say 30 mA RCD should trip between 15 mA and 30 mA, there are some which instead of between ½ and full current claim between 90% and 100 % but what we are saying is having a car charger could result in the RCD not giving the required protection, and with the Pod Point charger it says "As of the 1st January 2019 either a Type B RCD must be used or a Type A with 6mA DC protection included in the Pod-Point (see detail on packaging to determine what protection is required)," so it seems manufacturer date is important as the 6 mA trip for DC was only included after the 1st Jan 2019 and it is likely other makes are the same, so no one but the guy installing and reading the installation instructions for that charger knows if a type A or type B is required.

But the big point I am making is to simply plug in without checking on requirements is not good enough.

Aragorn84 · 30 Mar 2021

The pod point your quoting from is a wall mounted charger designed for permanent installation. They added the DC stuff when the 18th edition came out AFAIK, and clearly yes, these are designed to be installed by a professional electrician who can (should) check these things and ensure its all correct.

Plug in "granny" chargers however are intended to be used like any other portable device. IE jammed into any old socket by someone with zero electrical knowledge, so its not really the same thing, is it? I guess you would need to refer to the MI's of the portable charger, but i would expect one of the portable units should be able to be used anywhere without any issues.

JohnW2 · 30 Mar 2021

Aragorn84 said:
Youtube video time?

I've got that T-shirt

Probably the most useful one is flameport's which eric has just linked to and quoted. That shows that 50 mA of DC can (just over) double the trip threshold of a Type AC RCD (from 30 ms to 70 ms) - which I find reasonably credible. It's the 6 mA which eric suggested that I find far harder to believe.

Furthermore, the other important thing I have also been unable to find out is the possible extent (if any) of DC components of current due to equipment in normal operation (rather than under fault conditions)

Kind Regards, John

Aragorn84 · 30 Mar 2021

JohnW2 said:
Furthermore, the other important thing I have also been unable to find out is the possible extent (if any) of DC components of current due to equipment in normal operation (rather than under fault conditions)

There seems to be panic around the fact that theres a big DC battery... But something like a industrial motor drive inverter runs AC into a big DC Bus running 600+volts, and no-ones jumping about with those incase some of the DC sneaks out into the mains?

bernardgreen · 30 Mar 2021

In the test rig in the video the DC component appears to be added to the sensor by a third wire. This is the grey wire through the ELS sensor and the grey wire going to the RCD's third phase connections.

Hence the magnetic effect is not exactly the same as the magnetic effect that would happen if it was a DC current flowing through the sensor in one direction on the Live conductor and then coming back through the sensor in the opposite direction on the Neutral conductor. The two magnetic fields due to the two equal but opposite DC currents would cancel each other out and the sensor would not be magnetically saturated.

Only if the DC currents on Live and Neutral were different due to a leakage of DC to Ground would the DC affect the operation of the sensor.

Or am I missing something ?

JohnW2 · 30 Mar 2021

Aragorn84 said:
There seems to be panic around the fact that theres a big DC battery... But something like a industrial motor drive inverter runs AC into a big DC Bus running 600+volts, and no-ones jumping about with those incase some of the DC sneaks out into the mains?

Indeed. It may be simply due to ignorance on my part, but I have yet to really understand a lot of the excitement/'panic'.

Kind Regards, John

bernardgreen · 30 Mar 2021

This would be my test rig to test the reaction of a DC current on the operation of an RCD when there was no leakage to ground.

From this basic circuit additional components could be added to create a DC unbalance through the sensor.

JohnW2 · 30 Mar 2021

bernardgreen said:
In the test rig in the video the DC component appears to be added to the sensor by a third wire. This is the grey wire through the ELS sensor and the grey wire going to the RCD's third phase connections. ... Hence the magnetic effect is not exactly the same as the magnetic effect that would happen if it was a DC current flowing through the sensor in one direction on the Live conductor and then coming back through the sensor in the opposite direction on the Neutral conductor. The two magnetic fields due to the two equal but opposite DC currents would cancel each other out and the sensor would not be magnetically saturated. .... Only if the DC currents on Live and Neutral were different due to a leakage of DC to Ground would the DC affect the operation of the sensor.

Yes, I also wondered about that.

Hopefully flameport can clarify but, as you say, on the face of it, it looks as if what was being tested with was an L-N imbalanced DC current , which would presumably only ever arise if there were at least two faults in the connected equipment. However, as you say, maybe we are both misunderstanding the test setup and/or 'missing something'.

Kind Regards, John

ericmark · 30 Mar 2021

See how this boiler stipulates type A RCDs

must be employed where additional protection is required. I think 'addition protection' means where it is a TT supply, but not sure, it could be simply because a mid position valve may be used,

Clearly a diode is used to stall the motor, however the problem is not so much that it need a type A, F, or B but we really don't know the risk when using a type AC. We have had DC equipment for years, old cathode ray tube TV's with volt droppers (big resistors) often using half wave rectifiers, and it was also a good method to get half power.

We have never had RCD protection without some DC, so big question we all ask is what has changed?

Supplies to caravans and boats for years had to be TT, and the fire regulations ensured think from memory 2.6 meters from buildings, and an electric car is no different to a caravan, so want a TT supply, however can't use a TT supply as often too close to the house, so another method had to be found, when the method of dealing with an electric car fire is to put whole car in a container of water, not sure I want one closer than 2.6 meters anyway, it seems there is an effort to play down the problem but videos like this

are not helping, and I know petrol and diesel cars can also catch fire, but rare when simply parked up.

JohnW2 · 30 Mar 2021

ericmark said:
View attachment 228730I think 'addition protection' means where it is a TT supply, but not sure ...

That's almost the opposite of what BS7671 means when it specifies that "additional protection" is required. It refers mainly to those situations in which 30 mA RCD protection is required 'in addition to' the primary fault protection provided by OPDs in a TN installation. In other words, the 30 mA RCD is required "in addition to" the fault protection provided in a TN installation

In a TT installation, the only fault protection is obviously that provided by RCDs. If it is provided by 100 mA RCDs then, as with TN, BS7671 requires that there be the 'additional protection' of 30 mA RCDs in many situations (sockets, buried cables, lighting etc.) - but if the only RCDs in a TT installation, then they are obviously "the" protection, and not 'additional' to anything else.

Kind Regards, John

ericmark · 30 Mar 2021

So you only need a type A with TN and with TT type AC is good enough. Some thing seems wrong!

JohnW2 · 30 Mar 2021

ericmark said:
So you only need a type A with TN and with TT type AC is good enough. Some thing seems wrong!

Yes, I can't believe that is their intention, but it's the conclusion one might come to if one took literally what I wrote.

I suppose one could say that BS7671 still regards 'required 30 mA RCD protection' as being "additional protection" even in a TT installation (with no >30 mA RCDs) in which it is not "additional" to anything else. Indeed, I suppose that's essentially how it is written, since it always uses the term "additional protection" to refer to 'required' 30 mA RCD protection.

In terms of your boiler MIs, I'm sure what it means that a Type A must be used "when 30 mA RCD protection is required" (regardless of earthing type) - and I suspect you also understand/believe that, even though you brought "TT" into the discussion.

Kind Regards, John

ericmark · 30 Mar 2021

We seem to have lost @Bubbauk it was not my intention. He can likely use any black cable, black as it resists UV better, and 1.5 mm² is ample for 13 amp.

Likely he needs to change the type AC RCD for a type A or if a high integrity CU fit a type A curve B RCBO. Needs to be careful the RCBO is type A RCD not type B which should be better but in most cases it refers to the curve not type.

I am not sure as to the real need for type A RCD and I am sure you can see from what has been said others question also the need for type A, but looking at around £35 to change and personally I would play safe and change it.

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