Ask Me Help Desk - 55 amps #8 wire run 50 feet

Rotten... I will try to address your last post as politely as I can, but I am sure you will take it as an insult. You said that you were the most qualified but you do not understand the basic ampacity of wire, or the severity of the situation. A 100 amp panel requires a minimum of #2 wire. # 8 is rated at only 45 amps, and at that distance you should be using a 40 Amp breaker. If that is not enough, then you need to replace ALL the wire. And you should be using 4 wires, not 3. Again I suggest you hire someone more qualified than you to asses the situation.

Allow me to correct myself... for service #4 is allowable, as Stratmando suggested.

First solid wire is a wire made in one single solid strand.
Stranded wire is a wire made up of many smaller strands twisted together. Stranded wire is more flexible than solid wire.
Sounds like you have single conductors not made up into a cable. That's not the same thing as stranded wire. A wire is a wire, a cable is two or more wires (insulated) in an outer covering.

The maximum amperage of a wire is a factor of its size and the type of insulation used.
Apparently you have THW/THHW wire.

Maximum amperage of #8 THW/THHW (90 degree temp rating) wire is 55 amps. Maximum amperage of #6 THW/THHW (90 degree temp) wire is 75 amps.

Hopefully these wires are in some kind of conduit.

Mexico may let you get away over loading these wires but nature won't.

You can splice on a larger wire to the three foot of smaller wire but you still can not exceed the maximum amperage of that section of wire. To do so will cause that section of wire to over heat and cause a fire.

The maximum breaker size you can safely use must be sized for the size and type of wire that in the wall that you can not change. The breaker must be a double breaker, that is a double breaker with a single handle or a double breaker with two handles tied together so that when one trips off, both will trip off.

Disregard the ampacity of #8 wire at 90 Deg C, as this only applies if the terminations are rated 90 Deg C.

#8 THW/THHW is rated 50 amps, period.

If you change the wire to a larger size, you must replace the 3 feet of wire in the concrete.

Quote:

Originally Posted by rottenrichard00

What is the temp on the wire for 75/90 ?

#8 NM cable must use the 60 deg/C column, regardless of what it says on the cable.

LISTEN to the others.

Quote:

Originally Posted by rottenrichard00

...., I am probly the most qualifyed with in 1000 miles,

This is an extremely scary statement! :(

Good morning Richard.

Let me see if I can reiterate our concern for your installation.

Lets start with the load you want to service.

You want to drain 100 amps off a main service panel and send it to a sub-panel in an adjacent building.

The NEC 2008 code "Requires" that you use a individual conductors or a 3 wire cable (with ground) that is rated for 100 Amps. { If this panel was your main service panel then table 310.15 could be used and #4 copper conductors would be appropriate. But it is not. You need to use table 310.16 because this is a feeder for a sub-panel.}

Using table 310.16 you should select #1 copper conductors if you are running individual conductors or a cable rated for 100 amps (a 1/3 with ground).

Now to your breaker. A 100 amp breaker cannot service a cable rated for 50 amps. This a serious fire hazard. The 100 amp breaker will not trip and protect the circuit in time to prevent a fire. PERIOD.

A dual pole 100 breaker delivers up to 100 amps on each ungrounded conductor (HOT). It is not delivering 50 amps per conductor to total up to 100 amps.

Also, the only way to deliver a full 100 amps to the circuit would be to use a "Fully" rated circuit breaker and I do not believe that there are any residential breakers that carry the "Fully" rated listing.

Normal practice here is to only load a breaker to 80% of its fully rated load. For example a breaker rated at 100 amps would actually service a load of 80 amps. Less would actually be better but I believe the practice is to use the 80% mark.

Another problem is that you say the cable is directly buried in concrete. That will have to come out of the concrete because #1 copper is a much larger conductor than #8 and the fill requirements require a larger conduit to hold the larger cable.

I do not pretend to know or understand Mexican requirements for electrical service but what you have installed is clearly extremley dangerous and must be corrected.

One other thought, if you are using an underground feed to the sub-panel, I would strongly urge you to place the new cable into conduit from the main service panel to the panel. I suggest you use Schedule 40 PVC.

I make this suggestion for two reasons. 1 - the protection of the cable itself and 2- if the cable does get damaged, it would be easier to replace the cable by pulling a new cable through conduit then retrenching the run to find the break.

Quote:

Originally Posted by donf

Okay, you are officially scaring me.

The length of cable that passes through concrete, is it in conduit?

If I read one of your responses, you are using only 240 VAC. None of the connections at the sub panel will need 120 VAC?

The piece I cannot get to is not in any conduit, just cement, is this bad. I know it would never pass any code, but is it safe, the only thing that can burn/melt would be the wire,

The fire if it were to occur within the concrete certainly not damage the concrete.

However, because you are using a 100 amp breaker (which should service no load larger than 80 amps) will not react to ground faults or shorts fast enough to protect what ever is downstream of the breaker.

Let's be absolutely certain that you are tying a 100 amp breaker from your service panel and not trying to the feed from one home to feed a second home.

I promise you that I am not looking to just find work for you to do. That concrete block needs to broken up and removed and the proper sized cable needs to be run.

Fire danger is very real, not just something we are harping on.

Quote:

Originally Posted by Missouri Bound

Rotten....I will try to address your last post as politely as I can, but I am sure you will take it as an insult. You said that you were the most qualified but you do not understand the basic ampacity of wire, or the severity of the situation. A 100 amp panel requires a a minimum of #2 wire. # 8 is rated at only 45 amps, and at that distance you should be using a 40 Amp breaker. If that is not enough, then you need to replace ALL the wire. And you should be using 4 wires, not 3. Again I suggest you hire someone more qualified than you to asses the situation.

No worrys bro, Iam learning, I can't get mad at someone that knows more than me about this subject, and is willing to share.
First all my cable is in conduit execpt for the 3 feet in the cement.
(2) I can't hire anybody because I am building me a grow room, lose lips sink ships.
I would never use a 100amp breaker, I need about 40 -50 amp per side, so a 40 amp dubble pull with #4 cable should be cool ? I am using 54amps, 13amps, 10amps. Split it between the two hots , is what 38amps per side ? Am I on the right trac ?

Sorry, but if you are planning something that is illegal, I'm off this post.

Quote:

Originally Posted by donf

Sorry, but if you are planning something that is illegal, I'm off this post.

No nothing like that, I think I 've figured it out, thanks

Just for giggles, what's the Ampacity of #8 in free air? Anyone?

TW and UF is 60, THW, THHW, THWN and XHHW is 70.

Strat... it varies depending on the wire... THHN is 80 amps (copper)

I did not mention THHN can take 80 amps, as that is under the 90 Deg C column, which will refer to the temp rating of the terminations, and my experience is that 90 Deg C rated connections are rare and special order, being exclusively designed for heavy industrial applications.

This must be said, to prevent a DIY'er assuming 80 amps could be allowed anytime.

Thanks Missouri and TK.

Actually, I think that information like that, as TK eluded to tends to confuse anyone not familiar with basic electrical knowledge. As far as wiring applications go, it's always safe to follow the basics... 15 amp,; 14 ga. 20 amp; 12 ga. 30 amp; 10 ga... and so on.

[QUOTE=donf;2356990]

You guy are making it confusing, I know you mean well, thanks .
What is the Temp rating on the wire for, outside temp ? Max temp for wire ?
If I have A/C 13 amps, A/C 15amps, A/C 15amps,20amps.
Now, I need a total of 63 amps, I have the#8 wire and a 220 service. If I split it up, say 35amps a side I should be able to keep the wire I have. Is that how it is figured ?