3phase question

[paul_h]

Hi guys, I'm mainly a housebasher but done a few bigger jobs when serving my time. In past two years I've wired my dads pals car garage. Nothing major just wired an office some extra lights etc also wired 3 3phase car ramps.

Now the problem/question I have is when testing circuits everything was fine also checked phase rotation everything was great. But when actually testing the ramps 2out the 3 ran backwards ( up was down /down was up) when this happens I was always told to rotate the last two phases ( l2/l3) so i done this and ramps worked. Tested the phase rotation and it was showing up 321 instead of 123 on my fluke mft? So obv this would be classed as the phase rotation being reversed? Now I'm abit stumped because as I said my tests showed all rotation going same way and correct etc but yet still ramps ran backwards?

Am I missing something? :sad_smile:

 

[Darkwood]

You check phase rotation in 3 ph premises to confirm all 3phase mains and submains are sequenced the same, when connecting loads like motors etc its common to find they may be in reverse and where this is the case just swapping any 2 phases at the outgoing of the isolator or incoming of the ramp controls will suffice.

Reverse phase rotation isn't an issue unless different 3ph sockets and dist' boards etc are opposite to each other.... hench plugged in loads will work correctly in some sockets and backwards in other (if phase rotation conscious of course)

 

[telectrix]

as above. swap 2 phase round on the ramps, not the supply.

 

[Guest111]

Sometimes you can get a phase crossed at the incomer,seen that before but as Darkwood said so long as all the 3 phase sockets are wired the same then don,t worry too much

 

[paul_h]

Sorry shoulda made that clearer was just at the ramp I reversed the last two phases not at the db or isolator. Just thought I musta been missing/doing something wrong. Next question to follow on is same garage is getting a 3phase compressor. Just a single phase one there at the moment. I'm planning on using a 3phn&e commando socket and plug. I'm presuming it will have a flex on it (compressor hasn't been ordered yet) is there a chance the compressor will run backwards ? Apart from phase rotation is there any other tests I could do to make sure I've got it going the right way? Don't fancy getting it wrong ! Never wired up a 3phase compressor before lol

 

[telectrix]

all depends on how the compressor has been wired. best way is to connect up, switch on, and see which way it runs. reverse it if necessary. ( that is after you've done dead testing to ensure it's safe to energise ). one thing i'd suggest is to make sure the motor is connected in star configuration. if it's dual voltage and you connect it in delta, you'll bugger it.

 

[Guest111]

Basically just wire the socket up as normal l1 from supply to l1 in socket same for l2to l2 and l3 to l3 then make sure you get wires right way around on compressor and off you go.You will not do any harm to it if you get it going backwards,again just reverse 2 phases.Incidentally you probably wont need a neutral at the compressor they normally just use 3 phases and earth,hard to say if it will come prewired some do some don,t.

 

[paul_h]

Basically just wire the socket up as normal l1 from supply to l1 in socket same for l2to l2 and l3 to l3 then make sure you get wires right way around on compressor and off you go.You will not do any harm to it if you get it going backwards,again just reverse 2 phases.Incidentally you probably wont need a neutral at the compressor they normally just use 3 phases and earth,hard to say if it will come prewired some do some don,t.

this is what I was planning on doing thanks.

thanks for all the replies guys.

 

[telectrix]

suggest you use a 4 core SWA to feed the socket. then if you need a N, you can use the armour as cpc.

 

[Guest111]

suggest you use a 4 core SWA to feed the socket. then if you need a N, you can use the armour as cpc.

Nice one Tel usefull tip there for him

 

[GLENNSPARK]

when carrying out a phase rotation test you need to test for correct sequence at all connections on that circuit......as its easy for..lets say L1 and L2 to cross for a portion the circuit....then revet back to correct sequence at point of use..

 

[Knobhead]

Had the test had shown phase reversal at the service head, what would you do about it?

 

[Darkwood]

Id have dug the road up disconnected the supply cable ,turned it around so the cores line up in the correct order when ready for termination.... then sacked the cable team who layed it in backwards ... seen this loads times on upgrades when they couldn't physically splice into the main line on the street in the correct sequence.

 

[Knobhead]

Easier to just cut the cable and then tie it back together with a nice double bow.

 

[Sintra]

Had the test had shown phase reversal at the service head, what would you do about it?

That would be every service head in Belfast then.