Earthing of vehicles

[JelleM]

Hello 

My name is Jelle. I'm a belgian 3rd year bachelor student working on a schoolproject. The project consists of a modification of a truck. This modification contains electrical components at 230V AC. The problem is, these electrical components need proper earthing to prevent danger. Normally an earthing is provided but this is quite difficult in a truck because there's no connection with the earth. I know it's possible to use the chassis as a GROUND, but that's just a zero reference voltage so it's not the same as an Earthing connection.

My question is: how do I ensure the safety when using 230VAC components that need earthing which is not (or is it?) possible on a moveable vehicle.

Thank you in advance

Sincerely

 

[studiot]

Whilst I have some reservations helping you with this, as you should not be working on 230 volt circuitry unless you or someone in your team has the competence, I will offer a couple of pointers.

 

The Earth is not part of the working 230V AC circuitry and is, in fact not used in mobile equipment.

Instead you should employ double insulation methods throughout.

What is  not clear is the purpose of the 230V circuitry.

Is it a permanent installation supplying some on board equipment or is it providing a connection point for portable equipment?

[JelleM]

Thank you for your reply.

To start with, I'm designing this project, commissioned by a company. This means, if this design gets through, people with the right competences will be working on these electric circuits (not me).

The purpose of the 230V circuitry is to power electric motors via a motor controller (frequency drive). For our design, AC motors seem to be better.

Double isolation is indeed an option, but frequency drives don't work well without earthing because the earthing act as a filter.

Do you suggest to change our design and use DC motors instead?

 

Edited April 21, 2018 by JelleM

[Bender]

Joking aside : if it is filtering you want, the ground/chassis should do.

If it safety you want: ask someone who knows about the regulations and best practices, not some anonymous dudes on an internet forum. I'm sure one of your supervisors or professors can help.

[studiot]

3 hours ago, JelleM said:

Thank you for your reply.

To start with, I'm designing this project, commissioned by a company. This means, if this design gets through, people with the right competences will be working on these electric circuits (not me).

The purpose of the 230V circuitry is to power electric motors via a motor controller (frequency drive). For our design, AC motors seem to be better.

Double isolation is indeed an option, but frequency drives don't work well without earthing because the earthing act as a filter.

Do you suggest to change our design and use DC motors instead?

 

 

You didn't make clear if these motors are part of the vehicle system (eg hydraulic pump) or extra equipment you plug in (eg mounted camera rotator).

In aircraft a 400Hz supply is often used because the higher the frequency the smaller and lighter the motors and transformers.

Frequency drives? Is this to vary the speed of the motor? You did mention safety not filtering?

Filtering? Does this mean your drive circuitry is square or pulsed wave? How about incorporating some better filtering? Gyrators? High value capacitances also readily available these days.

You also need to consider the possibility of fault conditions energising exposed metal parts at supply voltage and the possibility of sparks.