# Ground size vs. Ungrounded Size



## Bob Badger (Apr 19, 2009)

Conduit Phil said:


> Why is an undersized ground wire acceptable in larger circuits? 15 amp needs #14, 20 amp needs #12 and 30 amp needs #10 - all full size grounds. Yet when you get up to 40 amp, you only need a #10 ground. Why?


Because it can handle the current for the short time it takes to open the breaker or fuse.

When you have a fault to the EGC even on a 20 amp circuit the current goes far above 20 amps until the over current device opens


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## Conduit Phil (Nov 19, 2009)

Bob Badger said:


> Because it can handle the current for the short time it takes to open the breaker or fuse.
> 
> When you have a fault to the EGC even on a 20 amp circuit the current goes far above 20 amps until the over current device opens


Well by that reasoning we should be able to have undersized grounds on circuits smaller than 40 amp then? Well, I know they used to. My parents house is wired with #14 that has #16 ground.


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## kancerr (Apr 16, 2010)

Conduit Phil said:


> Well by that reasoning we should be able to have undersized grounds on circuits smaller than 40 amp then? Well, I know they used to. My parents house is wired with #14 that has #16 ground.


are you sure its a ground and not a bx tension wire?


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## Conduit Phil (Nov 19, 2009)

kancerr said:


> are you sure its a ground and not a bx tension wire?


Yes, its a ground wire. The house is wired with NM, not BX. There was a discussion about this on here the other day. NM had undersized ground in the late 60s.


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## Ocularpatdown (Apr 27, 2010)

Conduit Phil said:


> . NM had undersized ground in the late 60s.


Yup, and in my house they wrapped that small ground wire back out of the box and attached it to the outside of the box with a ground screw that protrudes into the box right at the top in which a large device (dimmer/timer/GFCI) hits it


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