The top row of circuit breakers in the photo above violates Article 240.81 of the 2011 NEC. They’re operated vertically so they must be “ON” in the up position.
When is mounting panelboards horizontally acceptable?
To answer the question directly, it is acceptable when there’s no other practical solution. Mounting panelboards horizontally is permitted by the NEC when a vertical orientation is impractical. In general, panelboards must be mounted vertically whenever possible and in most cases they can be.
There are situations though where top to bottom clearance will restrict you from positioning a panel vertically. For instance, behind the access panels under some restaurant service counters. These often have a large number of appliances like; coffee makers, toasters, microwaves, and coolers.
In these kinds of applications there isn’t enough height to mount a panel vertically. Not one with enough circuits anyway. It isn’t practical to run individual circuits to these counters many times either. Mounting the panelboard horizontally is the only practical solution.
Here’s what you need know when mounting panelboards horizontally.
Mounting panelboards horizontally will cost you some breaker space. You will only be able to use the circuit breakers on the bottom row of the panelboard. The NEC requires that circuit breakers be “ON” in the up position when operated vertically. So you will only be able to use half of the panelboards circuit capacity.
Aside from the NEC requirements, look over the equipment and any literature that came with it. You want to make sure that a horizontal orientation isn’t prohibited by the manufacturer’s listing and/or labeling.
Lastly, consider positioning the panelboard so the door mounts on the cabinet to open downwards. This way it won’t need to be held up when accessing it.
Tell us about any installations where you had to mount a panel horizontally.
Related articles with the code references on EC&M‘s site
Mike Holt Article – owner of Mike Holt Enterprises
Mark Ode Article – staff engineering associate at UL