Fixed wiring Installation - Use of SY & YY Cables

[damoville]

Hi all,

Interested in the groups interpretation of BS7671 with regards to the used of SY & YY cables.

We have a commercial installation where we have a power supply installed to an air handling unit/ventilation plant.
The power supply supply to the AHU isolator is installed in SWA cable.
The load side to the AHU is installed in a SY screened cable as requested by the manufacturer.

Now, is the load side part of the fixed wiring installation or not? in my opinion is is not, however there are differing opinion across the industry.

Thoughts please.

Thanks in advance.

 

[MJPD29]

It is hard wired to the load side of the isolator, to a fixed object, in my view it would be part of the fixed wiring. I cant really see how it wouldn't be.

 

[James]

I would look at it the other way.
the control panel isolator is the end of the fixed wiring.
from there on, it is part of the appliance (even if the appliance is large with many motors etc)

sy cable may have been specified by the manufacturer to shield hf noise from inverter drives or fast switching ssr’s so the system remains emc compliant.

the sy cable should not be relying on any protective devices of the fixed installation and should be protected by breakers etc inside the control unit.
again, this bolsters my argument that the cables are not part of the fixed wiring.

 

[damoville]

I would look at it the other way.
the control panel isolator is the end of the fixed wiring.
from there on, it is part of the appliance (even if the appliance is large with many motors etc)

sy cable may have been specified by the manufacturer to shield hf noise from inverter drives or fast switching ssr’s so the system remains emc compliant.

the sy cable should not be relying on any protective devices of the fixed installation and should be protected by breakers etc inside the control unit.
again, this bolsters my argument that the cables are not part of the fixed wiring.

thanks James.

 

[James]

As you can see, there are different ways to look at this.
sometimes it is near impossible to get a majority vote amongst trained professionals!!

 

[Lucien Nunes]

Welcome to the forum, @damoville! We like people asking awkward questions so stick around.
Is the isolator part of the AHU and supplied with it, or obtained separately and installed on the wall next to it? I'm not sure that knowing the answer to that will nail it completely but it seems relevant to whether the SY cable then forms an integral part of the AHU once completed on site.

 

[James]

I was originally imagining a control box with multiple cables running out of it to several fans around a building.
reading it again I think it is a single piece of equipment.

either way, I still consider the end of fixed installation to be generally the isolator at the end of the supply cable.
from isolator to equipment I think of as an appliance flex.

 

[westward10]

What is stopping you from using this style of cable.

 

[cliffed]

It’s still not recognised in BS7671… but used all over the place.
Seen portable cabins cabled in it… external use prohibited
Its probably easier to install but there are alternatives