RCD type with an iBoost+

[JohnW2]

I would suspect that the output is referenced to the input.

If that is the case, then it merely begs the question as to whether or not the 'input' is earth-referenced.

If one side (or some intermediate point) of the output isn't connected, directly or indirectly, to earth, then the concept of 'Live'-earth faults/leaks obviously does not exist,and no type of RCD could serve any useful purpose.

Kind Regards, John

 

[JohnW2]

This is the point I was making, I have no idea, and I would suspect most people fitting them have no idea. To my mind with a TN supply the RCD is extra protection, and should it not work, then we still have the same protection as before the RCD drive, so no big problem.

That's true IF the 'supply' is earth-referenced. If it's not then, even if the 'supply' were AC, no RCD could provide any sort of protection. 'additional' or otherwise - and, as I said, if the supply is 'smooth DC' (no pulsating or varying component), then, even if earthj-referenced, nothing but a Type B RCD would provide any protection.

Kind Regards, John

 

[ericmark]

I expected it to work like a dimmer switch, I know it can reduce the current used so only uses excess power, it was only when reading the instruction I noted the reference to DC.

That's all I know, not a clue what 1B refers to, which is why I linked to the instructions from the start.

 

[JohnW2]

View attachment 332314 That's all I know, not a clue what 1B refers to, which is why I linked to the instructions from the start.

That would seem to move the goalposts quite a long way.

I don't know what "1B" is, either (and Mr Google doesn't seem to know, either), but if it's 'pulsed DC', with any sort or PWM, then a Type A RCD would presumably be adequate, the Type B only being needed to detect residual 'smooth DC' currents. Of course, all that still relies on the output being earth-reference - if not, no type of RCD would achieve anything.

Kind Regards, John

 

[Murdochcat]

Does it actually need a RCD ?

Ditto

 

[Why Not Indeed]

Type 1B probably refers to the contacts in the thermostat. These both claim to be that.

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[JohnW2]

Type 1B probably refers to the contacts in the thermostat. These both claim to be that.

Possibly - who knows?

However, I rather doubt it. Thee iboost instructions posted by eric that this it must be used with a "good quality working mechanical thermostat" - which implies that the thermostat is to be user-supplied, hence the iboost spec could not refer to it. Furthermore the "1B (Pulse Width Modulation)" in those instructions rather implies that the "1B" relates/refers to the PWM in some way, doesn't it?

Kind Regards, John

 

[plugwash]

If that is the case, then it merely begs the question as to whether or not the 'input' is earth-referenced.

Well the "input" is connected to the grid.

The way I see it there are three plausible scenarios for how the output is set up.

1. The output is floating. No RCD will have any effect on faults with the output wiring.
2. The output is independently referenced to earth. A RCD on the input side will not see faults on the output side.
3. The output is referenced to the input, which in turn is referenced to earth at the substation. A fault on the output side will drive imbalance currents through any RCD supplying the input side.

I don't know which one this device is, but I strongly suspect 3.

 

[JohnW2]

Well the "input" is connected to the grid.

Is it? The instructions eric posted says:

"..... The Solar iBoost+ output must be the only supply to the immersion heaters ...."

... which I took to mean that the 'input' was only ever from the solar installation (probably DC), never from the grid. Did you interpret it differently?

The way I see it there are three plausible scenarios for how the output is set up.
1. The output is floating. No RCD will have any effect on faults with the output wiring.

Agreed. I've said that a number of times.

2. The output is independently referenced to earth. A RCD on the input side will not see faults on the output side.

True, but, if it were the case, then an RCD on the output side would see downstream faults.

3. The output is referenced to the input, which in turn is referenced to earth at the substation. A fault on the output side will drive imbalance currents through any RCD supplying the input side.

As above, I read it as indicating that the supply never came from the grid, hence not connected to the substation. That does not, of course, preclude the possibility that the input (or output) might be deliberately connected to earth within the installation.

If the output were earth referenced, whether directly or indirectly, then, as per (2), an RCD on the output side would see downstream faults. However, contrary to what you say, I don't think an RCD on the input side would see any 'output side'faults, would it (since the non-earthed side of the input would presumably be isolated from the output)?

I don't know which one this device is, but I strongly suspect 3.

As above, I'm not so sure about that, not the least because I'm far from convinced that 'the grid' is part of the equation. However, like you, I do not 'know'.

Kind Regards, John

 

[plugwash]

Is it? The instructions eric posted says:

... which I took to mean that the 'input' was only ever from the solar installation (probably DC), never from the grid. Did you interpret it differently?

I think that just means that you should not try and run a direct supply to the immersion heater bypassing the iboost.

The "general scheme layout" diagram in the installation instructions clearly shows that the "solar iboost" is supplied via the mains wiring. The wiring diagram also says the device should be supplied from a "16A MCB or 13A fused outlet". It's pretty clear this thing is intended to take it's power from the mains wiring, not directly from the solar panels.

A current clamp on the meter tail is used to determine when there is excess solar generation and that information is sent wirelessly to the iboost.

I don't think an RCD on the input side would see any 'output side'faults, would it (since the non-earthed side of the input would presumably be isolated from the output)?

I don't know for sure how they built this thing, but given that the input is AC and the output is pulsed DC, my educated guess would be something along the lines of.

Input -> Bridge Rectifier -> PFC boost -> primary capacitors -> PWM switching -> output.

If so, then any earth fault currents in the output would nessacerally also flow in the input.

I doubt the "line" and "neutral" sides of the input are treated any differently from each other.

I doubt there is any isolation between input and output, including such isolation would add significant cost and bulk.

 

[JohnW2]

The "general scheme layout" diagram in the installation instructions clearly shows that the "solar iboost" is supplied via the mains wiring. The wiring diagram also says the device should be supplied from a "16A MCB or 13A fused outlet". It's pretty clear this thing is intended to take it's power from the mains wiring, not directly from the solar panels.

Fair enough. I haven't seen any of that,so perhaps need to look.

I don't know for sure how they built this thing, but given that the input is AC and the output is pulsed DC, my educated guess would be something along the lines of.
Input -> Bridge Rectifier -> PFC boost -> primary capacitors -> PWM switching -> output.
If so, then any earth fault currents in the output would nessacerally also flow in the input. .... I doubt there is any isolation between input and output, including such isolation would add significant cost and bulk

If there's no transformer involved, I would agree. I clearly need to try and discover more about what goes on inside these things. Watch this space!

Kind Regards, John

 

[ericmark]

Sorry the iboost+ is fed from main consumer unit 50 Hz supply. It has a wireless CT coil which will turn it on when export is detected, it does not use the DC direct from solar panels.

Neither can it work if there is no grid power, my main CU will get no power with a power failure, only my central heating and 4 sockets in kitchen used for freezers will still work.

Even lights will fail with a power cut, we have torches for that.

 

[JohnW2]

Fair enough. I haven't seen any of that,so perhaps need to look. .... If there's no transformer involved, I would agree. I clearly need to try and discover more about what goes on inside these things. Watch this space!

@plugwash ... OK, I've had a look at the installation manual (which is the best source I've so far found), and it seems to indicate that what you said is correct.

It's less sophisticated than I had thought. As you implied, it seems to simply use any 'spare' grid-synchronised output of the solar inverter to power the immersion - one consequence of which is, as eric has said,it will not work during a power cut.

That being the case, you're probably right that not only is the unit's output earth-referenced by virtue of its input but also that there is no input/output isolation of the non-earthed side. If that's the case then, as you said, a (Type A or 'above') RCD on the input side of the unit would see any faults downstream of the unit.

However, although it now seems that the above is true, if (as he has suggested) eric really feels the need to have RCD protection of the immersion then (assuming only that the output is earth-referenced), the surest way of achieving that is to have an RCD on the output of the unit -and, since it's pulsatile DC, a Type A RCD should be adequate for that.

Kind Regards, John

 

[flameport]

These immersion boost affairs are the equivalent of a PWM lighting dimmer connected to the immersion heater.
230V AC input, output is a chopped sinewave.
Input current will follow the chopped AC output.

Just like lighting dimmers, minimum of a Type A RCD required assuming you are having an RCD at all.

 

[DetlefSchmitz]

230V AC input, output is a chopped sinewave.

They claim it is modulated dc - do you have other information?