Connecting Machine to 3 phase isolator switch

[Andy Bradbury]

My isolator switches are 3 phase + neutral. My compressor requires 3 phase + PE. Can I use the neutral as a PE?

 

[Andy™]

no. there shoud be a cpc there though. you could however use the blue as a cpc if you move it to the earth bar and sleeve as necessary, but then you loose the neutral if you need it...

 

[Andy Bradbury]

Thanks for the quick reply. I thought that would be the case. I have just moved to a commercial building with 3 phase, which is new to me.
There are a number if Isolators dotted around the building which is handy. However none of them include an earth. It just seemed odd to me why someone would take the trouble to install all of them with no earth? Is it acceptable to use the cable armouring as a cpc?

 

[Fleeting]

The armour of the SWA cables if correctly connected is generally suitable as the cpc for general final circuits.

 

[ProDave]

It would be highly unusual not to have an earth. Care to post photographs of the isolator with the cover off

 

[Andy Bradbury]

Sure, I'll post some pics tomorrow. After some googling, and your kind help, I now know enough to know that I don't know what I am doing.
I think I'll call a professional. I just did'nt want to wait for 2 weeks for an electrician to come and connect 4 terminals.

 

[Andy™]

It just seemed odd to me why someone would take the trouble to install all of them with no earth? Is it acceptable to use the cable armouring as a cpc?

the armour is the earth... maybe it would be best to wait the 2 weeks

 

[Andy Bradbury]

Got it. I was looking for a yellow/green wire. I will take your advice and wait the 2 weeks.
Just out of interest though how would you connect an earth cable to the armour in the isolator switch?

 

[Phoenix]

If its a plastic cassed isolator, then whoever fitted it, ought to have fitted a link to the earth terminal off the banjo tag https://www.electricpoint.com/media...5mm-brass-spare-banjos-for-swa-gland-kits.jpg

or they might have used an earthing nut https://uk.rs-online.com/web/p/earth-protection-accessories/7000818

If its a metal clad isolator, then while the same is still good practice, you might also find it with just a banjo tag bolted to the case (which forms the earth path), you might even find it with just the paint scraped off under the gland (which is ok as long as its a decent job), there might also be some out there with no earth continuity because the paint hasn't been scraped off!

Post a picture and we will tell you what has been done and if it looks right or not

 

[Andy Bradbury]

It's a plastic isolator. There is no bonding tag. I like the look of those earthing nuts. Looks like it should be straightforward enough.
However a after reading the installation manual of my compressor, to avoid damage I need to make sure the motor spins in the right direction. I understand there can be an issue if the phase wires are not correct. Is this something that is checked when installed at the consumer unit? or pot luck. How would you confirm the right direction? I had no idea how complicated this subject can get! Thanks to all that have given me advice.

 

[Sharpend]

You need a phase rotation tester

 

[Andy Bradbury]

lol. I need an electrician! Anyone in the Reading area?
I thought I only need to connect 4 wires that's only 1 more than a 3 pin plug!

 

[Andy™]

short version, pot luck. phase rotation tester ca check rotation at the terminals of the isolator but depending on compressor wiring it may still go wrong direction. most comrpessors will be fine wrong direction for a few seconds to check although some wont

 

[Andy™]

lol. I need an electrician! Anyone in the Reading area?
I thought I only need to connect 4 wires that's only 1 more than a 3 pin plug!

but your 3 pin plug probably doesn't have 400v going through it. there's a lot more to it than just sticking a few wires in some terminals

 

[ProDave]

Unbelievable that whoever connected that isolator switch did not at least fit a banjo and earth lead to the earth terminal. I am struggling to think of any 3 phase class 2 machine that does not need an earth.

 

[Andy™]

chances are it did need an earth but they were less concerned about it than OP is

 

[Andy Bradbury]

The previous occupier of the building was an engineering company. With lathes and milling machines etc. I am assuming he had all the 3 phase isolators installed at the locations of his machinery. I did find it odd that there was no obvious way to earth them. Using the cable armouring sounds like a good enough idea to me, but non of the isolators have any evidence of that. The only other explanation I could think of is if there was a seperate cpc that has been removed?

 

[Sidewinder]

Another thing that is odd about this, is that the gland thread looks like it's rusty, so steel.
I've never seen a steel bodied SWA gland.
That said, if it is a BW or CW, then adding a banjo and fly lead may be all that is required.

 

[kerching]

I spotted the rust and assumed it was a 25/20mm reducer or maybe a nipple / coupling/ locknut combo as there was no bush available ( I've done similar when short of materials )

On a side note .....why is there never enough space in rotary isolators?