I am replacing my entrance panel combo with a larger 200 amp service. The panel I am installing is a surface mount, the existing panel is a flush mount. I am using surface mount because I can't drill a 2 1/2 inch hole in my top plate and I want it surface mount to make installing grid tie solar easier. The panel has all the knockouts on the back bottom and bottom. My wires enter the existing panel from the top so I need to either lengthen the wires or drill holes on the inside top area of the panel so they will reach. Is it ok to drill the extra holes I need and can I just drill one or two large holes and run all the wires through them using the romex clamps and bushings. Any thoughts appreciated.

  • You can, but I don't know the constraints, so I'll let someone else answer. There are tools to cut new knockouts.
    – Jay Bazuzi
    Mar 9, 2012 at 8:25
  • Not sure where this comment will end up. I have the ok from the electric co and a permit, have the grounding and bonding done, am installing a welder outlet, then will get the power shut off and install the panel. The panel I bought is a compromise, I couldn't find exactly what I wanted. If I can't make holes at the top back of the panel I will have to add another box to splice extensions on to all the old wires in. Does anyone know what section in the code deals with the rules for adding holes to a panel and splicing wires. Thanks to those who have replied.
    – Dave
    Mar 9, 2012 at 23:12
  • It sounds like you bought a bottom feed panel, if there are no KO's on top. Is there a removable plate on top to mount a hub to? If you bought a bottom feed panel the power company will not connect to because the UL is for bottom. A top feed will have a hub blank on top that you remove and mount the correct size hub. Another thing about drilling in a panel is if you are drilling in the power company's section or the end users section. Power company will not allow any holes in their section. Their side must remain 'factory fresh'.
    – lqlarry
    Mar 10, 2012 at 0:12
  • @Dave - see my edit2.
    – SteveR
    Mar 11, 2012 at 13:12
  • Its a bottom or top feed panel, with a removable plate for the hub. I intend to use the top feed, I assume there are no holes in the top section because it is an outdoor surface mount. The meter section is on the left and the breakers on the right, separate sections. I am hoping I can use an old panel and install it on the inside wall for a splicing box. I would have to make a cover for it to keep it accesable. I don't like splicing wires so that will be my last resort,
    – Dave
    Mar 11, 2012 at 17:42

3 Answers 3


It should not be a problem making a new hole for the service cable, but you should check you local codes. Where you make the hole depends on other factors, that a licensed electrician would know. This is done with a Knockout punch, not a hole saw. If you try to use a hole saw, you will only make a mess of it. A good set of KO punches are expensive. You can get cheaper sets, that will work a few times before they get dull such as this one or maybe you can borrow one. If you need to go from 3" to 2-1/2" then you may be able to use a doughnut (if code allows it!) reducing washer.enter image description here

This is quite an ambitious job for a newbie! I suggest you hire an electrician. You can not just add a bigger panel to the service, the lines at the house drop need to be sized bigger and possibly the lines to the house from the utility. You will need to change the wires from the meter, and then you can go through the back of the panel and forget about the KO hole. There will undoubtedly be code upgrades like grounding, that need to be implemented as well. And then there is a final inspection, and yes you need it, if you want your insurance to pay off in the event of a disaster.

Putting all the Romex wiring through one hole is not acceptable. You can put as many as two through an approved (for two Romex cables) type connector. Also "bundling" of cable has restrictions as well, usually only 2' at a point. Romex must be stapled before entering the box (usually within 12"). Again, You need to find the NEC (US) code and local code requirements.

If you still are thinking of doing this yourself, I would apply to your town hall for an electrical pre-inspection. An inspector will come to your house and you can lay your plan out to him. He will tell you if things need to be done different. You as a homeowner can file to do electrical work on Your own home. After the work is done the inspector will return and hopefully give you an approval. Nice and legal, and your insurance co. will accept it!

EDIT: Here is another cheap KO set with smaller sizes. Note that electrical hole sizes are not dimensional, such as a 1/2" electrical KO is actually a 7/8" hole, and takes a 3/8" Romex connector!

EDIT2: It may be possible to use a junction box and a raceway to the new panel. A raceway can be say a 3" conduit connecting the two, or an approved raceway. The splices would be made inside the Jbox to single conductors going through the raceway into the new panel. You could ask for a pre-inspection meeting to see if your inspector will accept this. If not he may offer other solutions. It is hard to evaluate your situation without seeing the whole picture.

  • 1
    A Step drill bit can be used for knockout holes.
    – Tester101
    Mar 9, 2012 at 13:53
  • @Tester101: that's a tough way to make a big hole!
    – Jay Bazuzi
    Mar 10, 2012 at 9:07
  • @SteveR That same KO set can be gotten from Amazon for $260: www.amazon.com/Greenlee-7238SB-Slug-Buster-Knockout-Ratchet/dp/B000LDGN5C/
    – Michael
    Jun 17, 2012 at 17:21

You can drill a new hole in the top of the panel. You would need to make sure that you will have enough room for bending the conductors for their termination point. A weather tight connector should be used to prevent any moisture from entering the enclosure.

  • 1
    Please read the FAQ on Self Promotion
    – ChrisF
    Jun 15, 2012 at 21:23

There are some hole saws and stepped drill bits which can be used to drill in sheet metal. I have used them with the purpose of creating knockout whereas there was none at a particular spot. The stepped drill bits, as the one shown below, will also deburr the hole for a nice finishing.

enter image description here

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