I havel looked in t-300.5 and found 18" why does the UF cable have to be protected if it is direct burial cable. Isn't the intent to have the insulation directly in contact with the soil? It kind of defeats the purpose of the cable insulation disign.
18" is only allowed if it is under some form of concrete (see the column on the left with the application). If it is anything else it is 24". Yes, you can direct bury it and that is the column you would use. If you protect it you don't have to dig as deep. "Life is a series of trade-offs"...protect the wire or dig deeper!
I understand your point but I don't see the column on the left which reads application. I think I am not seing something. Can you directly point me to the right language which supports your statement. I have looked into notes and I don't really see anything specific. I looked all other locations but it does not seem to relate to my question because this is clearly a residential property. I column that I am going of is One and Two family dwelling...for dwelling related purposes. I have consulted an electrician and he looks at it the same way I do. I don't see what I am missing. I have also looke into article 340 and found nothing specific. Waiting for your input.
Paulp, 1st,look at the top of Table 300.5 It says "Type of wiring method or circuit". The only one that fits a 240v direct bury circuit is column 1 "Direct burial cable or conductors". Then look on the left side titled "Location of wiring method or circuit". The only one that fits is the one titled "all locations not specifically listed below. It says 24". What column and row are you trying to use that is giving you 18"?
I saw all of that but my point is, is that this is a residence. This is not a location that is not specified. This is clearly and a One family dwelling. The column that I was going off is 6th from the top or 2nd from the bottom. I realize what you are saying but again my point is the location is specified. (Residential) The column reads, "One- and Two- family dwelling driveways and outdoor parking areas, and used only for dwelling-related purposes". The part of the quote that seems to fit the criteria is "dwelling related purposes. The statement seems to give a little more room for argument. I am not trying to be stubborn. And I do agree that it is better to burry the unprotected cable at 2'. I just don't see how this could apply to the column which reads "All locations not specified when this is clearly a residential property which is a One family dwelling.
Paulp, I think you are taking the phrase out of context. This says ...driveways and parking areas used ... It does not refer to any place around a residential single family dwelling. You will notice that column 4 also speaks of residential, but limits the circuit to 20 amps, gfi protected, 120 volts. Everything in the left hand column refers to some form of protection (condrete, pavement, a building, etc.). This allows you to reduce the cover requirements. Unless this circuit to the AC is running under the driveway or under a parking area, it does not fall in this catagory. Since you want to bury it in the ground with no protection, you must go 24" If it were put into RMC it could go 6" deep or if it were in PVC it could go 18" deep. This table used to give the cover requirements and then gave exceptions to reduce the cover by a certain amount of inches for different methods. Then in a code revision they made it "easier" to understand. I agree this is a residential property, One Family Dwelling, but it is not under the protection of a residential driveway or parking area.
HLC, You have a valid point that the cable has to have more protection. I realize that a driveway or a parking area would normally be paved which would allow less burial depth. I wish the code would be a little more specific. This area seems to throw many people off. I apreciate your patients.