inverter saftey

Submitted: Wednesday, Feb 05, 2014 at 18:25
ThreadID: 106099 Views:1517 Replies:2 FollowUps:11
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in another post it was suggested that a fully isolated type of inverter is preferable (safer) than a non isolated type,could someone advise how we can differentiate between the two types,thankyou.
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Reply By: Allan B (Member, SunCoast) - Wednesday, Feb 05, 2014 at 19:37

Wednesday, Feb 05, 2014 at 19:37
Hi Pepper,

You need to use a multimeter on the OHMS position.
The Inverter should be disconnected from all external wiring, both input and output.
First, with the meter switched on and the probes separated, it should be reading "OL" or similar. Then join the probes together and it should read close to zero such as 1 or 2 ohms which is the resistance of the meter leads.
If there is a switch on the inverter, turn it ON.
Now connect one probe to either of the input terminals and the other probe to one side of the 240v output socket. The meter should still read "OL" or a very high resistance such as 5 or more megohms (M ohms)
Repeat the test with the leads on the alternate terminals in turn. The reading should be as above.
If the reading at any time is low, that is less than several megohms, then the inverter cannot be considered as "Isolated".

If unsure about the above, get your friendly electrician to test it. He will do it in a couple of minutes and, if he is a good guy, will not charge you.

Cheers
Allan

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Follow Up By: pepper2 - Thursday, Feb 06, 2014 at 09:26

Thursday, Feb 06, 2014 at 09:26
thankyou for the reply,will go and test mine.
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Follow Up By: MactrolPod - Thursday, Feb 06, 2014 at 15:15

Thursday, Feb 06, 2014 at 15:15
That has raised some questions.

Shouldn't all inverters be isolated from the DC input side to the AC output side?

If the AC output side is isolated from earth/ground/vehicle then you can not get a shock from a live AC output to the metal body of the vehicle.

If the Earth terminal of the AC outlet is bonded to the metal body of the vehicle then it is also bonded to the negative of the DC input there for not isolated.

Do you need a RCD safety switch in any or all of the above?

I think I have confused myself LOL. Seriously though I know nothing about inverters, just hook mine up to DC and use it.
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Follow Up By: MactrolPod - Thursday, Feb 06, 2014 at 15:18

Thursday, Feb 06, 2014 at 15:18
I was thinking about the isolated power supply Dad had in the shed, used before double insulated tools came on the market.

So to me isolated meant the AC output was isolated from earth, just like that transformer did in Dads power supply.
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Follow Up By: Allan B (Member, SunCoast) - Thursday, Feb 06, 2014 at 17:05

Thursday, Feb 06, 2014 at 17:05
Yes Mac, all inverters sold now (and in recent times) are, or at least should be, isolated.

This isolation expression refers to the live (L1 & L2) 230v output of the inverter. As the 12v negative is earthed to the vehicle body then if the inverter metal housing is secured to the vehicle body, so the housing is connected to 12v negative, but that's OK. So long as the 230v side is isolated from the 12v circuit and from the metal housing.

The earth pin of the 230v outlet socket is connected to the metal body of the inverter and if this is then in contact with the vehicle body as a hove, then this ensures that any Class 1 appliance (Those with metal housings connected to the earth pin) will be equipotential with the vehicle body so no voltage can be developed between them. This is better than not being bonded but not as good as Class 2 (Double-insulated).

Do you need a RCD? No, because being an isolated 230v live circuit (Not connected to earth or the vehicle body) no current can flow to earth hence a RCD is neither necessary nor can it operate in most normal circumstances. I just hope this does not fire-up another RCD debate!

You Dad's "isolated power supply" is exactly the same as an isolated inverter.

Cheers
Allan

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Follow Up By: Racey - Thursday, Feb 06, 2014 at 17:25

Thursday, Feb 06, 2014 at 17:25
Allan B, you have hit the right spot regarding isolating the 12 volts supply from the 230 volt output. Up until 6-7 years ago there inverters on the market which had a feed-back connection from the output to input. The problem was highlighted when someone on a building site was electrocuted when making contact with the 12 volt side. I can't remember the exact details but that's the guts of it. Following that incident a new Australian Standard was developed to overcome the deficiencies of the non-isolated inverters. There should not be any non-isolated inverters currently on the Australian market. For this reason I would be reluctant to buy an inverter from O/seas on fleabay without knowing the full specs.

Cheers
Jon
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Follow Up By: oldtrack123 - Thursday, Feb 06, 2014 at 22:32

Thursday, Feb 06, 2014 at 22:32
HI Allan
RE [quote]"Do you need a RCD? No, because being an isolated 230v live circuit (Not connected to earth or the vehicle body) no current can flow to earth hence a RCD is neither necessary nor can it operate in most normal circumstances. I just hope this does not fire-up another RCD debate![end quote ]

YES, a RCD cannot function

Perhaps ADD the safety recommendation?

ONLY CONNECT ONE CLASS1 device at any time
PeterQ

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Follow Up By: oldtrack123 - Thursday, Feb 06, 2014 at 22:38

Thursday, Feb 06, 2014 at 22:38
HI Macropad
Do you remember the SAFETY recommendation that came with those "SAFETY PAKS"

Only connect one CLASS 1 device
NO DOUBLE adaptors
On two occassions, I actauly saw the results of using double adapters & Class 1 tools
ONE,a very nasty shock
Ambulance job & the other a real shake up.
PLease consider the SAFETY RECOMMENDATION


PeterQ
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Follow Up By: Allan B (Member, SunCoast) - Thursday, Feb 06, 2014 at 23:11

Thursday, Feb 06, 2014 at 23:11
Better still, avoid Class 1 altogether and only use Class 2 (Double Insulated) appliances.
Cheers
Allan

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Follow Up By: oldtrack123 - Thursday, Feb 06, 2014 at 23:52

Thursday, Feb 06, 2014 at 23:52
HI Allan
Totally agree with that
where

PeterQ
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Follow Up By: MactrolPod - Friday, Feb 07, 2014 at 06:04

Friday, Feb 07, 2014 at 06:04
Oldtrack, now that's a long time ago.
We had at least one when I started my apprentiship in 1974.
When double insulated tools were introduced the factory bought them, we did have a huge metal case drill that need the safety pack but don't remember the recommendations, it's a long time ago... LOL
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Follow Up By: oldtrack123 - Friday, Feb 07, 2014 at 16:23

Friday, Feb 07, 2014 at 16:23
HI Mactrol pod


The "Safety Paks" came onto the market about mid/'late 1960s
IF my poor old memory serves me right

RCDs ,called 'Earth leakage core balance circuit breakers" 'at that time came onto the Aus market market earlier, aroundf the late 50s early 60s ,again if my memory is correct
KLockner Mueller was the brand that the company I worked for
[as head service technician] sold

PeterQ
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Reply By: Kevin.Hutch - Sunday, Feb 09, 2014 at 13:24

Sunday, Feb 09, 2014 at 13:24
I think the specifics of the question have been accurately covered.

The key is shown in the labelling L1 & L2 is for Live 1 & 2 and they are both isolated from earth.

In the Australian domestic situation all wall outlets are marked A (Active with respect to ground) and N (Neutral with respect to ground).

Live is "Live" where as Active is Live with respect to ground.

When you go to an isolated wiring system such as for an inverter or portable generator or caravan, with little chance of a good earth connection, load circuits are double pole switched to prevent a fault connecting L1 or L2 to ground being in the non switched side of the circuit.

In addition if those load circuits could be connected to a MEN (Multiple Earth Neutral) system they are required to have an RCD even though in the isolated system the RCD can not trip from Residual Current as there is no earth return.

Kevin H
AnswerID: 526041

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