Three phase earth 'rod'

[imago]

I went to look at a job the other evening on a farm which had barns converted to storage and light industrial units. I was there to look at wiring up one of the units for socket outlets and lights. When I got there I was pleasantly surprised to see a brand new meter for each of the four units along with new SWA feeding a brand new hager DB in each.

So I measured up, and sorted out what they wanted where, added up the figures then went back for a closer look at the supply. Four feeds from the main DB all with new switching so isolation won't be an issue. Everything looked new and shiny including the 16mm earth cable, but then I noticed that it was curled into a pig tail and went behind the pallet I was standing on. I moved the pallet which turned out to be the lid for the earth pit. I say earth pit, I mean hole chisled into the concrete floor of the barn. I moved the pallet and found that the end of the cable was clamped to a 3/8" rod, and noticed that the top of the rod had been hacksawn off. I didn't get the meter out of the van, I'll leave that pleasure for a return visit.

If I get to go back I'll take a few pictures, but I'll have to put a warning in the title so that those of a squeamish nature don't look!

I couldn't help but wonder why anyone would have all that work and new kit, then stick in a screwfix special to try and get an earth. Never mind two metres from the building, smack a hole in the floor, that'll do. :crazy:

 

[Knobhead]

A two pole alternator produces 50Hz at 3000RPM

 

[Bobster]

It's only 3000rpm not really that fast.

 

[electric will]

That's revs per min not per second, say it was 3000 revs per second (wouldn't want to be stood next to it) that'd determine the 50 hertz with 2 poles, there must be many poles so power is generated many times per revolution, allowing the rotor to spin slower.

 

[Knobhead]

I give up!

 

[electric will]

Why give up, generator with 2 poles spinning at 1 rev per second surly would produce a frequency of 1 hertz? So to get 50 hertz you could say itd need to spin at 50 revs per second-not really possible but with multiple poles the out put would be produced more times per revolution?

 

[Guest55]

I give up!

not a week goes by on this forum without me feeling the same sentiment. ;-)

 

[electric will]

Explain to me then how to get 50 hertz out of a 2 pole alternator.

 

[electric will]

Sorry got it! 3000 rpm divided by 60 seconds comes to 50 so spinning at 3000 would produce 50 hertz

 

[Bobster]

Sorry got it! 3000 rpm divided by 60 seconds comes to 50 so spinning at 3000 would produce 50 hertz

The penny's dropped

 

[electric will]

Yeah penny's dropped, cheers for being so helpful, I was nearly there one of you could have put me right in one sentence, most people would not bother to understand how things work but I like to know, don't see why other members on here have to be so bitchy.

 

[Guitarist]

Yeah penny's dropped, cheers for being so helpful, I was nearly there one of you could have put me right in one sentence, most people would not bother to understand how things work but I like to know, don't see why other members on here have to be so bitchy.

I think it's great that you want to understand this stuff, as most electricians not from an industrial background have never even connected a motor, and they think "poles" are the guys trying to take their work.
This thread wasn't really bitchy at all tbh.... Now, if you'd asked what size MCB for 1.0mm cable, THEN you would have seen bitchy

 

[electric will]

I think it's great that you want to understand this stuff, as most electricians not from an industrial background have never even connected a motor, and they think "poles" are the guys trying to take their work.
This thread wasn't really bitchy at all tbh.... Now, if you'd asked what size MCB for 1.0mm cable, THEN you would have seen bitchy

Whats a Mcb?