3 phase generator questions

[zeroberto]

Some clarification please guys.

Got called out today to wire a 3 phase 32amp Socket into a Builders own 3 phase Genny - (ex AGrreko, bought at auction). Needed to supply a 3 phase plasterers pump system. The genny only had 2x 16amp 240v outlets.

So, opened panel, there was stud terminals L1, L2, L3 & N. Had prewired a board with small CU feeding a socket with 6mm tails coming out. connected these onto the terminals. Turned on pump - nowt.

To cut a long story short, testing with both martindale neon tester & Digital tester showed between 215/220v on all L terminals to N. So far so good. L1/L2 or L2/l3 or L1/L3 all 0V (expected around 415). Coming out of the N terminal was a 10mm earth wire secured to the body of the genny. when I test across this Earth terminal & any L, or for that matter N, then I get 110v which confuses me.

Can somebody explain how this works please?

btw once I worked out that L1/2/3 were the same phase (knackered genny obv) the builder hired a replacement, connected same way to new one and off we went. 10 minutes to do that. 4 hours between connecting original & waiting on replacement.

 

[mechelec]

are you sure it was a three phase genny? may sound a silly question but are you sure it was knackered as you was getting 220V at the stud terminals.

 

[zeroberto]

Its 6 foot long, 4 foot high & wide and with L1 L2 & L3 & N terminals I'm sure it is/was. should also have said that where the data plate was - can see the outline & the 4 rivet holes - someone has scratched "1 phase" which suggests its been adapted at some point. But anyone explain to me the readings I am getting - is this normal for a generator?

 

[Knobhead]

Without seeing it I couldn’t say and I’m not going to guess. But I’ll bet your mates bought a pup.

 

[Cyberprog]

The alternator may have had it's tappings altered to provide single phase output (Which normally is a higher rating for a single phase, than the 3phase, per phase, rating). You may just need to adjust it back to 3-phase, and you should be able to ring the alternator manufacturer and they'll tell you what needs to be done. It's a relatively simple job to do IIRC.

http://www.dieselserviceandsupply.com/Generator_Phase_Conversions.aspx has a reasonable description of what's involved.