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Old 06-28-2008, 03:32 AM   #1
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Any way round this?


I'm restoring a car and just bought a 4HP compressor. Only trouble is it trips the entire house as on startup its drawing about 17 amps.
Is there anything i can do to solve this problem?
please help, im working to a deadline..
Thanks

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Old 06-28-2008, 07:51 AM   #2
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Any way round this?


Sure, have a dedicated line run to it. Or find a 20A circuit that is not being used while you use the compressor.

You say the WHOLE house trips, as in the main breaker? You may have other issues that this situation is exposing.

Are you using this compressor on an extension cord? This could be a REAL issue as well.

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Old 06-28-2008, 10:13 AM   #3
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Any way round this?


Ok, i have found a spare cooker circuit, which i will try. the main breaker tripped, not the one fro that particular circuit. i wasn't using a lead.
s
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Old 06-28-2008, 10:14 AM   #4
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Any way round this?


Are you in the UK?
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Old 06-28-2008, 01:54 PM   #5
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Any way round this?


Is your unloader valve on the comp. working properly? If not it will try and start under load.
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Old 06-28-2008, 02:40 PM   #6
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Any way round this?


On start up a 4 Hp motor is pulling WAY more current than 17 amps.
A five hp motor at 120 volt pulls 55 amps running and the same motor at 240 volts pulls 28 volts. Values taken from the NEMA chart.
When a motor starts it can draw as much as 8 times the run current. For one, your breaker is to small. Look at the nameplate on the compressor. Look for FLA or full load amps, then multiply that number by 1.75. This gives you the correct size breaker in amps.
If it is truly only pulling 17 amps at start, there is another problem. How did you manage to measure the current. What kind of meter did you use. Something is very fishy about your situation.
Post the nameplate ratings. All of them, or better yet take a picture of the nameplate and post that.
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Old 06-28-2008, 03:31 PM   #7
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Any way round this?


I was told that i pulled 17amps by the guy i bought it off, he took it to a specialist in brum, they had it running and measured it there.
I am wondering to save making alterations to the house's wiring, (its not my house) if a good idea would be to replace the motor with a slightly smaller one.
Any ideas of what to look for?
cheers.
Steve
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Old 06-28-2008, 06:42 PM   #8
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If this is not your house you should NOT be doing any electrical work there.

At the same time I would NOT pout a smaller motor on a package compressor. They are designed to work together.

Are you in the UK?
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Old 06-28-2008, 08:25 PM   #9
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How long does it take to trip it? If it's immediate you may have a ground fault.
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Old 06-29-2008, 12:37 AM   #10
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Any way round this?


What brand and rating is the breaker that trips? For example, a 4HP compressor would likely trip a Crouse-Hinds 60, but not a Square D 100.

Does it trip right away, or after it's been running for a while?

If the running current on a motor is 17 amps, the starting current will be around 100 amps.

Rob
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Old 06-29-2008, 04:09 AM   #11
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Hi yeah im in the UK, the breaker is an RCD made by MK, the garage circuit says LN 5906 s B6
the main breaker, (which is what tripped) said RCD LN5780 s 80A 30mA

thats about all i know.
any ideas?
Steve
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Old 06-29-2008, 10:18 AM   #12
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What is on the name plate. We cannot help you until we know what you have.
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Old 06-29-2008, 08:06 PM   #13
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An RCD is I believe what we call a GFCI. Compressor should be on a normal breaker not a RCD/GFCI.

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