No earth

[ohthatshowyoudo]

Hi please can someone assist me.. i have started an inspection on a control circuit and noticed they have not run in an earth on a control circuit they run in a 3 core cable but taped up the green and yellow as live cable. the cable is run under ground from the distribution and is terminated within enclosed plastic houseing so there would be no fault on caseing. please can someone explain to me how i go about protecting this sort of circuit.... or does it require rewire ?

 

[Tester Steve]

Not quite sure what you mean here. Is the cable a 3 core cable, i.e. with brown, blue and green/yellow or are there three seperate cables? You say the g/y is marked up as a live, is this cable being used for three phases?

Steve.

 

[Guest123]

Is the cable an SWA, could the armour be providing the earth path???

 

[ohthatshowyoudo]

Hi steve the cable is a 3 core brown blue g/y but they have used the g/y as a live for a motor control circuit

 

[ohthatshowyoudo]

Hi lenny the cable is not swa but is of rubber sheath being used for control cuirct of motor

 

[Tester Steve]

Hi steve the cable is a 3 core brown blue g/y but they have used the g/y as a live for a motor control circuit

So I take it is being used for three phases. You said it goes underground, can you get at it to run a seperate c.p.c.??

Steve.

 

[ohthatshowyoudo]

Hi the 3 core is being used for control on start stop / main isolater wired back to panel for all of them. it is going to work out very expensive to dig up and replace i realsticly know that the chance of shock is nill, but if someone was to slice the cable how would i protect this with only lives ?

 

[Deleted member 26818]

What voltage if any does the cable carry?
Are the points the control cable serves earthed through other conductors?

 

[malcolmsanford]

Is the motor class I or II insulation.

There is no regulation stating a cable must have a CPC through it, we do have a regulation stating that there must be a CPC at each point of an installation.

Is this inspection part of a PIR, and if it is what are you going to code it, or are you advising remedial work, as replacing the cable.

 

[ohthatshowyoudo]

Hi spilondon the voltage is 220v 50hz its just plain control cable were as if you would wire a light switch you would also drop an earth in maybe for future use. i am just trieing to get my head around that in the case of a fault be it that someone was to cut the cable ( not likely to happen) but they they did without an earth i can not protect from short circuit. can i use rcbo or they only used for installations with high earth impeadance.

 

[Knobhead]

This is quite common on LV control, lazy yes but it’s a fact of life. A lot depends on the construction of the control station. Plastic enclosure, glands and buttons don’t worry about it. What are you going to earth?

 

[Deleted member 26818]

Yes you could use an RCBO which would offer protection against both an earth fault and short circuit.

 

[GLENNSPARK]

"if you would wire a light switch you would also drop an earth in maybe for future use." Eh? you "drop an earth in" because metal backboxes need earthing together with the 3.5mm screws (exposed conductive parts). It isnt just about "future use"..............

 

[ohthatshowyoudo]

Hi malcommsanford
the inspection is part of PIR.... if there are no other solutions then i will have to rewire the control units, its just i am trying to save the company money. i know somewere within the regs there is a bit on earth free zone but wanted any advice that could help me combat the situation without spending what will turn out to be thousands of pounds.

 

[malcolmsanford]

Earth free zones are under section 418.1 for non conducting locations and the first sentence will tell you that these are not applicable in this case,

Is this a control wire for just the starter assembly or is it the actual power top the motor?

 

[ohthatshowyoudo]

god damm server keeps dropping out................ malcolmmansford.... yes the cable is just control for start stops can i use an rcbo and put warning signs ?

 

[ohthatshowyoudo]

sorry glenspark i was refering to surface mounted plastic s/w i will be more specific next time

 

[malcolmsanford]

It's so difficult to get an handle on your set up.

From the DB board does it go to a local switch isolator of some kind? Does it have a CPC From the board to this.

I take it then that your 3 core cable goes from hopefully the local switch isolator to the motor control panel and from the control panel to the motor? is this right.

The control panel and the buttons etc as Tony said is most likely class II and so Ok, but what is your motor?

 

[ohthatshowyoudo]

the motor them selfs are earthed.... the control stations ie isolator /start stop are wired from the d/b in 3 core were they used g/y --- sw live out to equipment returning control back to db for switching of contactor and thermal overload. db has main earth and all other circuits are earthed.

 

[malcolmsanford]

Then I would not worry to much about it to be honest as Tony said this is something you will see often in control wiring.

 

[GLENNSPARK]

sorry glenspark i was refering to surface mounted plastic s/w i will be more specific next time

no probs mate (i shouldn`t jump the gun)lol!!!

 

[ipf]

I agree Malcolm. 3 wire stop/start control? If so, is it wired in flex, what cca? length of run? what mechanical protection underground?.

 

[ohthatshowyoudo]

thank you all