Pig tailing Paired screened cable

[WaterSparky]

Hi guys,

Was talking with a friend of mine, thats been snagged on on pig-tailing pair screened and overall screened cable before the actual cable enters the junction box (In this case a Rotork, with 2 x 4-20mA loops) His Commissioning engineer says its not allowed, I come from a maintenance background and find this brilliant as when you have to remove a instrument or actuator etc the pig tails are a god send. Essentially Im asking the question of what effect this would have, I can't see it being too bad seeing as it is Paired, Pair screened and overall screened? Ive done this nearly every time and never had a problem.

Regards

WS

 

[shanky887614]

his commissioning engineer is a bellend.

nothing wrong with it, we had to do it by the book when we did the training room and most controls were pigtailed.

we are talking we needed castle glands,metal tywraps, most containment types and most different gland types.

the guy was ott really, 1mm out of the end of all ferules etc

 

[Knobhead]

It depends on what the specification is. The commissioning team have to stick to it and will make sure you do.

 

[Bobster]

I've never seen an issue with it.

I have seen huge problems caused with people pigtailing profibus cable.

 

[bignod]

In work with me we never pigtail cables into rotork's or any other type of actuator. It is on a power station and have nearly 1000 actuators on site. Find it easier for fault finding if the cables are not pigtailed

 

[Bobster]

How does a pigtail hinder fault finding?

 

[shanky887614]

surely you are checking via the cores for electrical problems.

one of the reasons we use pig tails is, if there is a problem on the damper itself the mechanical guys/estates can remove it without turning off the panel or disconnecting the cables out of the panel

 

[bignod]

It is due partially due to our control schemes and due to cable runs picking up induced voltages even with screened cables

 

[shanky887614]

It is due partially due to our control schemes and due to cable runs picking up induced voltages even with screened cables

i dont buy that, if a small pig tail going into an actuator can pick up induced voltage you have bigger problems.


the screened cable should be kept seperate from power anyway so what are you guys doing?

 

[bignod]

A lot of cables share the same cable ways from 11kv to control cables on trays in same cable ways. It is the way the station was designed.can be a real headache on times following cables and tracing faults. Not pigtailing was a standard when the place was built 40 years ago.

 

[shanky887614]

A lot of cables share the same cable ways from 11kv to control cables on trays in same cable ways. It is the way the station was designed.can be a real headache on times following cables and tracing faults. Not pigtailing was a standard when the place was built 40 years ago.

nothing to say you shouldn't in regs then, im sure in regs its states segragation of circuits.


or are your controls 230v? we tend to use 12/24v controls.



fair enough if thats how it was done, not much you can do

 

[bignod]

Our controls can be 240 ac or DC down to 24v but are predominantly 50v DC . Being a power station we don't have to comply with the regulations, but use them as a best practice

 

[Bobster]

Dependent on the type of power station you work at, you will have to work to far more strict regulations. They aren't just best practice!

 

[Knobhead]

surely you are checking via the cores for electrical problems.

one of the reasons we use pig tails is, if there is a problem on the damper itself the mechanical guys/estates can remove it without turning off the panel or disconnecting the cables out of the panel

I wouldn’t buy that either. If an actuator was to be changed the valve gets changed. I don’t know what size Rotork’s the OP is on about but with most of ours the cables would get damaged unless disconnected.

It still comes down to what is in the specification and not what you think it should be.

 

[shanky887614]

I wouldn’t buy that either. If an actuator was to be changed the valve gets changed. I don’t know what size Rotork’s the OP is on about but with most of ours the cables would get damaged unless disconnected.

It still comes down to what is in the specification and not what you think it should be.

in our case quite often pipe fitters will change valves etc and that is one of the reasons we pigtail them.