Hazardous areas - control voltage transformer earthing -

[static zap]

Are you sure the secondary side of this tx is not centre taped to earth ie 55 - 0 - 55v?

How would we test for this ?
a) 2x identical suitable value Lamps , resistors in series . See if mid point is 0V ?
b) (or just load 55v to earth for possible problems)

 

[Pete999]

How would we test for this ?
a) 2x identical suitable value Lamps , resistors in series . See if mid point is 0V ?
b) (or just load 55v to earth for possible problems)

Measure Voltage across output terminals and from each output terminal to CP of TX

 

[Deleted member 26818]

If it’s center tapped to earth, then you would measure 55V from any one conductor to earth.
If the Neutral is tied to earth, then you would measure 110V Line to earth, and 0V Neutral to earth.
If you cannot measure anything to earth from either conductor, then nothing has been tapped or tied to earth.

 

[davesparks]

How would we test for this ?
a) 2x identical suitable value Lamps , resistors in series . See if mid point is 0V ?
b) (or just load 55v to earth for possible problems)

Read the label on the transformer

 

[netblindpaul]

CTE is not allowed in the machinery directive electrical product standard, so if it’s CTE then it is non compliant and probably illegal as it will not meet the EHSR’s.

 

[Cbuk2k2]

I've been in an ongoing debate regarding earthing of a control transformer and i'd like some other opinions.

690 primary, 120v secondary supplying control circuits (contactors/DC convertors etc), the neutral is tied to earth - My issue is the location that it is tied to Earth.

As far as I know the difference between a TN-S and a TN-C-S system is whether or not the neutral is connected to 'ground' at the source or further down the line.

60079-14 - 6.3.2 TN type of system earthing If a type of system earthing TN is used, it shall be type TN-S (with separate neutral N and protective conductor PE) in the hazardous area, i.e. the neutral and the protective conductor shall not be connected together, or combined in a single conductor, in the hazardous area. At any point of transition from TN-C to TN-S, the protective conductor shall be connected to the equipotential bonding system in the non-hazardous area.

Please see attached photo; The proposed design shows the point where the neutral is tied to earth (circled in blue) - this makes the highlighted section the 'C' in a TN-C-S system.

To create a TN-S system it would need to be where it is marked Red (taken directly off the transformer)

Also the highlighted cable is a line bushing from an Exd enclosure (which houses the transformer) to a close coupled Exe enclosure so this bushing cable would be combining the neutral and protective conductor.

Any thoughts agreeing/disagreeing? I can't seem to budge some peoples stance on it and to me it's black and white.

Cheers.

It’s fairly standard practice to be honest

 

[Pete999]

It’s fairly standard practice to be honest

I was brought up in the wrong era mate.

 

[Megawatt]

I've been in an ongoing debate regarding earthing of a control transformer and i'd like some other opinions.

690 primary, 120v secondary supplying control circuits (contactors/DC convertors etc), the neutral is tied to earth - My issue is the location that it is tied to Earth.

As far as I know the difference between a TN-S and a TN-C-S system is whether or not the neutral is connected to 'ground' at the source or further down the line.

60079-14 - 6.3.2 TN type of system earthing If a type of system earthing TN is used, it shall be type TN-S (with separate neutral N and protective conductor PE) in the hazardous area, i.e. the neutral and the protective conductor shall not be connected together, or combined in a single conductor, in the hazardous area. At any point of transition from TN-C to TN-S, the protective conductor shall be connected to the equipotential bonding system in the non-hazardous area.

Please see attached photo; The proposed design shows the point where the neutral is tied to earth (circled in blue) - this makes the highlighted section the 'C' in a TN-C-S system.

To create a TN-S system it would need to be where it is marked Red (taken directly off the transformer)

Also the highlighted cable is a line bushing from an Exd enclosure (which houses the transformer) to a close coupled Exe enclosure so this bushing cable would be combining the neutral and protective conductor.

Any thoughts agreeing/disagreeing? I can't seem to budge some peoples stance on it and to me it's black and white.

Cheers.

I don’t see a problem by bonding where you have circled in red. I have to agree with you why bond it again

 

[Bobster]

Well the most immediate problem I read is that you are using an Exe enclosure, with a supply that is not rated Exe.

So right off the bat this installation isn't going to comply.

At this voltage and power availability, Exd is the option you should be looking at.