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colingaffney

3 phase arcing

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colingaffney

I have a 3 phase installation arcing just above the main MCCB switch integral within a 250amp 3 phase hager fuseboard .

It is the buzz bar linking kit .

It has blown all 3 250amp fuses in the main head twice now .

On the 1st visit all 3 fuses had blown and nothing else and then the 2nd time all the fuses blew + the mccb switch had blown also .

There is no loose connection eg all nuts and bolts are tight and i'm getting more then 200m ohms if I test between the earth  and any of the phases or between any of the phases .

The strange thing is there is about 20 volts coming through one of the phases to earth even though the main fuses are blown .

The buzz bars are fairly damaged eg what looks like chipped at the edges presumably through arcing .

Does anyone know what this means .

Colin     

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Andy™

probably means you need a new board...

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Evans Electric

Any chance of a photo  Colin ?    

 

What sort of current is being drawn ?      Whats the rating  on  the MCCB ?   

You say you've checked all the B/bar  links ,   wondering if the MCCB is arcing ?   Is it a dusty atmosphere ?  

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kerching

You say all the nuts and bolts are tight.... thats as maybe BUT are they actually bearing down on anything?

i have had them in the past where they were tight but the bar they were connected to was as slack as a Wizards sleeve as thermal cycling had loosened the connection, then it arced, then the nuts welded them selves to the studs

 

just saying

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Tony S

The 20V across a fuse isn’t normal but not unknown. In the event of a short circuit the three supply fuses will clear the fault but fuses aren’t an exact science. Two fuses may blow, the third doesn’t see the full effect of the fault and makes a half hearted attempt but won’t fully blow clear. This makes them dangerous.

 

If two fuses blow always replace all three as the third fuse has been stressed and will fail in time.

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