Author Topic: Just bought a powerjack 15000, modding.  (Read 3723 times)

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Offline Fionn

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Re: Just bought a powerjack 15000, modding.
« Reply #75 on: April 25, 2017, 06:36:27 PM »
There will always be some earth current, unless you're floating in mid air, it might be micro amps but there will be some path to earth if the system is earth referenced.

The example you give is not really relevant to the safety of a standard electrical installation whatsoever in any case. You have created an insulated matting and adapted your behaviour to avoid creating earth paths by your own admission - hardly typical of the usage of standard electrical appliances.

Regardless, this is a moot discussion, I clearly stated in my post that protection would only be provided if the fault current exceeded 30mA.
We're in agreement so I don't see what we're adding to the discussion at this point.

Or are you in fact arguing in agreement with the OP that we should do away with earth referencing and RCD protection and go with unmonitored floating installations?

Offline welshman

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Re: Just bought a powerjack 15000, modding.
« Reply #76 on: May 19, 2017, 04:42:31 PM »
There will always be some earth current, unless you're floating in mid air, it might be micro amps but there will be some path to earth if the system is earth referenced.

The example you give is not really relevant to the safety of a standard electrical installation whatsoever in any case. You have created an insulated matting and adapted your behaviour to avoid creating earth paths by your own admission - hardly typical of the usage of standard electrical appliances.

Regardless, this is a moot discussion, I clearly stated in my post that protection would only be provided if the fault current exceeded 30mA.
We're in agreement so I don't see what we're adding to the discussion at this point.

Or are you in fact arguing in agreement with the OP that we should do away with earth referencing and RCD protection and go with unmonitored floating installations?

Thanks for your input, but at the end of the day the result of the situation is this..

I have gone from not being able to get a shock from touching the live wire to now being able to get a shock from touching the live because i've bonded the earth to neutral...

but everyone tells me i'm now safer.

i'm still trying to figure that one out exactly. ;)


Offline welshman

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Re: Just bought a powerjack 15000, modding.
« Reply #77 on: May 19, 2017, 04:44:50 PM »
In case anyone is wondering the system has been switching itself to charge/inverter mode daily upon startup of generator with the earth bonded to neutral for some time now and the fets have not blown as i had worried might have.

looks like despite the manual for the pj telling you to switch it off and on when the input power is established or lost the unit doesn't seem to blow up like they used to.

they must have done some clever stuff with the ramping up of the power on the newer boards.

Offline Fionn

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Re: Just bought a powerjack 15000, modding.
« Reply #78 on: May 19, 2017, 04:50:24 PM »
You're correct, until you have one fault your current system is safer.

The issues is that when that fault develops, you'll have no way of knowing it and then when you get a second fault it could be fatal.

It's essentially an IT type electrical system that you've created if you want to research that. They're used in industry where high reliability is required but always with a monitoring system that monitors resistance between live, neutral and earth at all times.

They're not really suitable for domestic general distribution due to the risks and the fact that faults can be hard to track down.

That's promising on the power jack boards, I've kind of converted to the EGS002 ones myself though myself.

Offline welshman

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Re: Just bought a powerjack 15000, modding.
« Reply #79 on: May 20, 2017, 03:06:09 PM »
You're correct, until you have one fault your current system is safer.

The issues is that when that fault develops, you'll have no way of knowing it and then when you get a second fault it could be fatal.

It's essentially an IT type electrical system that you've created if you want to research that. They're used in industry where high reliability is required but always with a monitoring system that monitors resistance between live, neutral and earth at all times.

They're not really suitable for domestic general distribution due to the risks and the fact that faults can be hard to track down.

That's promising on the power jack boards, I've kind of converted to the EGS002 ones myself though myself.

then i think we can all agree that if we had a device called a "neutral grounding resistor monitor" connected up, which would then trip the breaker if there was a connection between earth and neutral while leaving 'neutral' floating and not bonded to earth, we would have the safest system going?


Offline Fionn

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Re: Just bought a powerjack 15000, modding.
« Reply #80 on: May 20, 2017, 04:49:52 PM »
Yes I agree it would be very safe, however I believe such a system would be unworkable for general distribution for at least 3 reasons.

1. Cost - the monitoring devices are expensive, at least I'm not aware of any easily available inexpensive ones.

2. Lack of discrimination - A fault anywhere on the system has to bring down the entire supply. So your immersion heater for example could go faulty and that leaves you with no power until you track down the fault (which would take a while) and repair it. The more extensive your distribution the more complex this becomes.

3. False alarms - In order to be useful the system would be need to be set at a quite sensitive setpoint. Since you have to monitor the entire system as one, a long term deterioration in one or many devices could combine to lower the resistance to earth close enough that it could trip unnecessarily during periods of high humidity for example.

Hope that makes sense!



Offline MadScientist267

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Re: Just bought a powerjack 15000, modding.
« Reply #81 on: May 20, 2017, 04:51:17 PM »
then i think we can all agree that if we had a device called a "neutral grounding resistor monitor" connected up, which would then trip the breaker if there was a connection between earth and neutral while leaving 'neutral' floating and not bonded to earth, we would have the safest system going?

I believe that takes this full circle. Here, we call that a GFI/GFCI/RCD/PITA  ;D

I encountered this issue with the truck and it's umbilical cord connection, and wrestled back and forth with what was the best way to provision for every scenario I could think of... the answer? There wasn't one. Not that covered them all at least.

In the end, I went with looking at the truck as an "appliance" that has most of its threat potential inside of it, and gave it its own internal N-E bond, complete with a set of downstream GFIs. Once someone is inside, there's no more threat of getting zapped than in a normal everyday dwelling wired for AC.

The caveat to this is that because of the tires, it is for all intents and purposes inherently isolated from earth, as the "single appliance". The problem then became how to deal with bonding the frame to my upstream source's ground to keep it at earth potential, while keeping an upstream GFI happy under no-fault conditions. Put simply, it wasn't possible to do *both* internal and external safety protection to my satisfaction at the same time.

If the upstream connection is to a non-GFI protected source, the earth bond is more important than ever, because if I'm parked on grass or the asphalt is wet, there's a much higher chance that anyone with one foot on the ground and the other on the rear bumper will be part of a lower resistance path at both, than if it is parked on pavement and everything is dry.

Having the internal N-E bond however, this means that the normal current return path would share with the earth lead.

If there *IS* an upstream GFI (a scenario I only envisioned as likely to increase in probability of encountering), this results in an immediate trip of the GFI with nothing more than the *capacitive reactance alone* of the internal wiring connected as a "load".

As a side note, this was a bit baffling until I realized (and subsequently confirmed) that this was what was happening... the fluke was showing completely open resistance measurements, but that is done with DC. AC had snuck parasitic capacitance in under my nose. This however is ultimately moot, because even without it, the moment a real load gets applied, the same result happens.

What I ended up doing was placing a "jumper" in that could leave the truck frame and umbilical disconnect/breaker box bonded to the umbilical's earth, still leaving the internal bond in place to provide the protection on the inside. This of course then ultimately means that an open (or other) neutral fault between the truck frame and upstream source's N-E bond relies on the upstream GFI to prevent shock hazard conditions. Again, I weighed this against the idea that it's then essentially the equivalent of grabbing a toaster chassis in an up-to-code kitchen in terms of threat. GFIs fail too, after all, but that failure would need to be combined with the open neutral or other fault to become a problem.

Whether or not to have the jumper in place of course requires knowledge of the upstream system I'm connecting to... which leads me to a final point...

The thing I keep seeing here, and it's either overlooked, ignored, or rationalized away, is something that was ingrained in me early on: "Treat every wire as if it can kill you". You can rationalize and argue against the idea that its possible all day long, but get into an argument with physics, and (I really hope) I don't need to justify my reasoning for betting on my choice as to which one will win, right?

As for isolation transformers: Under the wrong circumstances, they *will NOT* save your neck. They're designed in general to isolate power and ground leakage to levels that *equipment* can safely tolerate, not people. Don't fool yourself into thinking otherwise. If you don't believe me, connect one with only the hot side connected to the appropriate primary terminal, and leave the neutral and ground disconnected... then check how much AC current is available between one of the secondary leads and earth...

You no longer have a transformer... you have a *capacitor*, a non-trivial one at that, which passes AC rather freely. Still think it'll save you?

</rant> </2cents>

Steve

Wanted: Schrödinger's cat, dead and alive.