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J187 08-15-2007 12:34 PM

Allowed to run more than one romex cable through a single hole in a joist?
My brother is running some 14-2 romex in his house. He needs to pass 6 or 7 romex cables through a joist and down toward the basement. Can he run more than one cable through a single hole? If so, how many? Thanks

KUIPORNG 08-15-2007 12:51 PM

I think the questions should be really , how large the hole can be drilled without affecting the structure...

it should be as many cables as the hole can hold.

when I did my basement, I have some place where need to fit a lot of cables to different holes.... I see no reason there will be any danger to anything...

J187 08-15-2007 04:21 PM

Is it in code to allow as many cables as the hole will allow?

johnny331 08-15-2007 05:59 PM

It's been 5 1/2 hours since you asked.... you could have called the inspector and had an answer in 30 seconds... I mean, that is why you waste, I mean, pay the permit fee for....

I prefer many smaller holes spaced a few inches apart in the center of the member, rather than a big 'ol hole with a half-dozen cables....

walt1122 08-16-2007 11:04 AM

Don't quote me on this and as another message suggested you might want to run this question by the electrical inspector... But a rough rule of thumb is that if you have any troble threading the wire throught the hole it's too full!! they should be loosely run to keep them from getting too hot. Electricity gives off heat. Heat = resistance, resistance = more heat... you get the idea. And if you need to add more holes better pose this question to the inspector too. Don't want to weaken the structure by placing the holes to close or to low.


Stubbie 08-16-2007 11:54 AM

Code does not directly address the number of cables that can pass thru a bored hole. The consideration for this has to do with deration and/or bundling. You will see all kinds of residential installations where there are 8,9,or 10 nm's run through a bored hole. There is even code that allows a conduit coming from a panel to be filled with nm's for not more than 10 feet under the right circumstances. In my area most inspectors don't like to see more than four 14/2 G or four 12/2 G through a bored hole. The reason for this is that if you were to derate the ampacity of the cables you still will maintain the 15 or 20 amps respectively for the wire guages. Over four 2 wire conductor cables and you would have to reduce the branch circuit ampacity if your inspector considers this to be a deration issue. Multiwires of 14/3G or 12/3G are essentially the same as 2 wire conductors as you do not have to count the neutral for deration purposes.
Hole size must be considered in joists... building codes allow a hole to be drilled any where on the joist as long as it does not exceed 1/3 of the joist depth. The bored hole must not be closer than 2 inches to the face edge of the joist. Generally........

2x6......bored hole max dia....... 1 13/16"
2x8......bored hole max dia....... 2 7/16"
2x10... bored hole max. dia...... 3 3/16"
2x12... bored hole max. dia...... 3 3/4"

As a side note in my experience where ambient temperatures are not overly exceeded like in an attic in Arizona when its 106F outside I don't believe 6 or 7 14/2's will be an issue as long as you don't have very high temperature considerations. If it is possible drill two holes then the problem goes away.


J187 08-17-2007 07:36 AM

Stubbie, Awesome info. I knew deration could be a consideration, but I wasn't sure at what point it became an issue. This helps immensely, Thanks. He will be very happy to see all those guidlines laid out for him.

JOHNNY - He tried, the inspector wouldn't give a clear response.

KUIPORNG 08-17-2007 08:46 AM

In my area... questions normally not go to inspector directly, as I understand... they are very busy and really difficult to answer phone calls... rather... it goes to the office people and they direct it to some sort of code knowledable people then come back with an answer... this all through emailing... I asked quite a few questions when I renovating my basement, they all got answered politely... but some answer is fast, some is not that fast... but not right away for sure...

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