Inverter/ Electrical Safety

[maxjj Senior Member Find all posts View Profile Close maxjj]

Hi all
With the increased use of 12V DC to 240V AC inverters and the build in inverter in the 150 , I just got thinking about the safety side of it.
I could imagine my wife plugging her laptop into the inverter and sitting on a chair or in the car while I am dragging the axe or shovel etc out the back and dropping it onto the 240v cable, or any similar scenario. I understand a bit about ac and dc systems, but this is out of my league.


Is the 12v dc sufficiently electrically isolated from the 240v AC or can the active 240V make a circuit with the car body and battery?
I would expect the body of the inverter in the 150 be connected to the body of car.
I am thinking that there is potential for a fault in inverter or cable that could cause the car body to liven up. Its not like there is an rcd to measure what is going in and out.

Would putting a multi meter in the active and the 240v Inverter and the car body/ "-" indicate anything?????

[Fozzy Senior Member Find all posts View Profile Close Fozzy]

Re: Inverter/ Electrical Safety

Tomorrow morning I'll hook my multimeter up and find out!

Cheers,

Dave

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

Re: Inverter/ Electrical Safety

For safety both the active and the nuetral of the inverter should be
isolated from the car body. This way the only way you can get electrocuted
is to go across the active and the nuetral as cars are not referenced to
ground as the mains grid is.

As for the general safety point, 240V is 240V and an inverter will kill you just as
quickly as the mains will!

There are also regulations laid down in respect to the installation of inverters in
vehicle to protect the safety of emergency services personnel who may have to
work on vehicles that have been involved in an accident.

Cheers

LeighW

[Hubble80 Member Find all posts View Profile Close Hubble80]

Re: Inverter/ Electrical Safety

I agree totally with LeighW, but to add something... I do not have an inverter so am unsure as to how the one you have is protected. I would assume (and hope) that they have protection (fuses or circuit breakers) on both the 12Vdc and 240Vac side of the inverter.

In the instance of dropping an axe or something of that nature on the 240Vac cable, it would trip the 240Vac protection. If there isn't any, a short circuit across the positive and negative would cause the draw on the 12Vdc side to be above it's current rating and either shutdown or operate any applicable protection device.

just remember that there is a food chain in protection of electrical circuits. 1st - The equipment, 2nd - the cabling and last of all YOU!!!! So relying on safety systems is not a good idea, we all need to exercise a bit of common sense around electrical circuits and cabling.

My 2c

Pete

[maxjj Senior Member Find all posts View Profile Close maxjj]

Re: Inverter/ Electrical Safety

cheers thanks for your replies,
I appreciate that the 12 v system of car is its own system and the 240 output of the inverter is its own, but is there sufficent electrical isolation between the 240V output - the active cable and the "-" of the battery and hence the car body.
If a fault occurs that exposes 240V active to the car body is there the potential for an electric shock?

[waltec Senior Member Find all posts View Profile Close waltec]

Re: Inverter/ Electrical Safety

cheers thanks for your replies,
I appreciate that the 12 v system of car is its own system and the 240 output of the inverter is its own, but is there sufficent electrical isolation between the 240V output - the active cable and the "-" of the battery and hence the car body.
If a fault occurs that exposes 240V active to the car body is there the potential for an electric shock?

Unfortunately the nature of the fault cannot be controlled, therefore you cannot determine the outcome of that fault, so yes there the chance that the car body could become active (but not in relationship to earth. Saying that you would require 2 faults to make that happen as invertors have isolated outputs ie no relationship between input and output, so you would need a fault to short 1 output (active or neutral) to car ground and then you would have to touch to other output, but if the two output shorted together it would trip the output overload. Basically the only way you can get electricuted is that you have to go across both active and neutral.

As one of the previous posted stated, it is still 240v and as such all normal safety measured must be obsurbed, ie avoid water, damage to cables etc.

Matt

[maxjj Senior Member Find all posts View Profile Close maxjj]

Re: Inverter/ Electrical Safety

That`s the bit I was thinking, that there is a chance the body could become live. I appreciate all the normal safety precautions are important, but there is nothing in the manual to give you any idea and I don`t really see the general public with an inverter being all that clued up about it. In some ways they can be more dangerous because of it, but then ignorance is bliss.
I am doing too much thinking, but then I work in the industry, think control room Powerstation ie Homer Simpson.

[Cruisin 120 Junior Member Find all posts View Profile Close Cruisin 120]

Re: Inverter/ Electrical Safety

I agree totally with LeighW, but to add something... I do not have an inverter so am unsure as to how the one you have is protected. I would assume (and hope) that they have protection (fuses or circuit breakers) on both the 12Vdc and 240Vac side of the inverter.

In the instance of dropping an axe or something of that nature on the 240Vac cable, it would trip the 240Vac protection. If there isn't any, a short circuit across the positive and negative would cause the draw on the 12Vdc side to be above it's current rating and either shutdown or operate any applicable protection device.

just remember that there is a food chain in protection of electrical circuits. 1st - The equipment, 2nd - the cabling and last of all YOU!!!! So relying on safety systems is not a good idea, we all need to exercise a bit of common sense around electrical circuits and cabling.

My 2c

Pete

Just to rehash this info ,
When looking at protection of an electrical circuit, protection is first provided for the cabling, then yourself taking into account what the installation is driving/controlling and last of all, the equipment is then looked at. cheers

[Matty80 Avid PP Poster! Find all posts View Profile Close Matty80]

Re: Inverter/ Electrical Safety

For safety both the active and the nuetral of the inverter should be isolated from the car body. This way the only way you can get electrocuted is to go across the active and the nuetral as cars are not referenced to ground as the mains grid is.

I think Leigh nailed it with this! Touching both of the active wires will result in a nasty electric shock, touching only one will not.

Consider this: A fault develops within inverter causing car body to become same potential as fault. A fault is present within an appliance, such as a steel encapsulated work lamp. Bear in mind that these faults alone may not trip the overcurrent or short circuit protection inside the inverter. if you touch both car and work lamp (no doubt, with different hands) then you have a situation that could be fatal.

Pluging the same work lamp in at home would trip your ELCB (Earth Leakage Circuit Breaker).

As standard and due to the nature of the inverter design, an ELCB does not function with inverters, as they do no contain an MEN (Main Earth Neutral) link, or additionally an earth stake connection to ground. Your appliances should, therefore, be checked for correct operation periodically by a licensed electrician.

Inverters can kill you just as quickly as a normal household mains supply!

If 30mA of current is considered to be dangerous and >80mA fatal, then even the smallest 100W inverter would have the potential to cause serious injury, or death through electricution, if such a shock is delivered across the heart.

In the instance of dropping an axe or something of that nature on the 240Vac cable, it would trip the 240Vac protection. If there isn't any, a short circuit across the positive and negative would cause the draw on the 12Vdc side to be above it's current rating and either shutdown or operate any applicable protection device.

I don't entirely agree with this, I assume when you say 'positive' and 'negative' you actually mean 'active' and 'neutral' of the 240v AC. While loading and unloading an inverter may affect the current draw on the supply side slightly, it is more likely that if the internal protection for short circuit failed, that it internals of the inverter (mainly MOSFET's, diodes, transistors and other ICs) would overheat and self destruct, destorying the inverter, without much effect if any on the 12v supply side fuse protection.

The protection within the inverter is designed to SOLELY to protect the inverter's internal circuitry. NOT YOU or the appliance. Same principle for household wiring - the circuit breakers in your meter box ONLY protect the cables in the walls. The ELCB is the only device designed to save your life.

Always check manufacture's documentation for correct installation procedures and follow the recommend safety guidelines.