My sub panel has three wires coming in. 2 hots and 1 to a floating neutral/ground bus bar. The gounds and neutrals are supposed to be separate correct?
Well depends…but I wont go into that because it confuses people. Anyway most Sub-Panels will have (4) wires coming in and yes a floating Neutral ( grounded conductor ) and the ground will connect to a bar directly in contact with the metal enclosure or as you stated on a grounding bar.
Yes, the Neutral and Grounding need to be seperated…
To better explain it would need a picture but as long as you always remember their should be (4) wires you are fine…just in some cases in older work and certain situations you may see (3) wires but should see a GEC as well…which in BOTH cases you should see that anyway if to a detached building…if the sub-panel is within the same structure as the main panel then it will have (4) wires going to it and installed as listed above.
I swear, all the mobile/ manu. homes this is what I see. A 200a main panel on a pole out in the yard with a 200a breaker in it. Then inside in the laundry room sub/load side panel, three wires coming in. You mean to tell me all have been wrong?
The metal conduit is commonly used as the fourth conductor - the equipment grounding conductor (EGC). There should be isolated neutrals in the panels of mobile/manufactured homes.
In your business I would recomend an evaluation of any main feeder that didn’t have a bonding jumper (where appropriate) or a wire for the EGC (4 wire feeder) if you can’t verify there is a safe path for fault current. Certainly using the metal conduit is legal but I would want someone to verifty the conduit and all the joints were OK. Around here buried EMT may not last a decade. It might trick your suretest but blow open in a real fault.
AS greg said…NEVER assume anything…the 4th wire should be present unless you can verify the the path for the grounding of the system.
Are they all wrong…well considering mobile homes…you would be SHOCKED how many are done wrong…never assume ANYTHING
So all sub panels have 4 wires to be correct? This is good to know.
Mark, that is correct, however here in Tucson, as you know, you will very seldom see a 4 wire feed to a subpanel that was installed prior to 1968. There was actually no code enforcement here prior to 1968. When we do an upgrade on the main panel, the inspectors do not make us re feed the subpanel, they will allow the 3 wire feed to remain (unless it is real simple like a back to back). On many older buildings there was only a meter outside and the interior panel was considered the main panel, alto that does not make the 3 wire feed okay.
However, when you are talking mobile homes, that is another story. It is very important for a mobile home to have a separate grounding wire not only for the subpanel, but for the range and dryer as well. If you are finding otherwise, you need to report it as not acceptable, regardless of the age of the installation. Of course on some very tiny trailers you will find a 3 wire feed but it will only be 120 volts, this is OK.
Around here buried EMT may not last a decade. quote]
Greg, here in the desert buried emt will only last 1-2 years. Even rigid will rust away in less than 20 years.
I feel it is very irresponsibe to use buried conduit as a grounding path, even if it is legal.
Thank you Thank you