200% Neutral Panel

Yes, the feeder must be 200% also.

Example: your bringing a 200A Feeder to a panel that calls for a 200% neutral, you would bring 2 1/2" with 3-3/0, 2-3/0 N, 1-#6 G

Just because you have a panel rated at a certain amperage does not mean you need to install conductors to match this rating. The conductors are sized for the calculated load. You may install larger conductors for future loads, but it is not required. In your example you may not have loads that require a 200% neutral.

Sometimes, in the single phase panel, the phase (or line) is spitted into two different buses. The loads are connected between the two buses with common neutral and the neutral carries the current from both line buses. This is done for the convenience of connecting breakers from both sides. In this case, the neutral bus has to be 200% capacity of each line bus. Maybe be this the case for the panel you are talking about.

- MS

mmsamad: on a single phase 240/120 volts the neutral would carry the unbalance current. if line L1 was carrying 50 amps, & L2 was carrying 40 amps the neutral would be carrying 10 amps, not 90 amps. perry

Perry,

The case that I mentioned is not 120/240V panel. It is only one voltage, either 120V or 240V. Two line buses are bolt connected in the panel and they are at same potential. The incoming to the panel is one line and neutral. If it is 120V panel and 12,000VA loads are connected to each of the line bus, the line bus current will be 100A but neutral current will be 200A.

As I mentioned, the panel may be of such configuration and it can be the cause of the 200% rating of the neutral bus, however the OP can look inside of the panel and verify if this is the case. The panel drawing (panel schedule) should have this information as well.

- MS

msamad; are you measuring from one bus to neutral? & the other bus to neutral to get the same voltage? every panel i have installed has the design voltages & amps listed. there are times where the neutral conductor only has to carry the unbalance current. 200 amps main line & a 100 amp neutral. perry

Dear Guest,

The panel is designed as per the load feeders and the type of load, not vici-versa. check whether the panel is used for UPS feeders. 200% neutral, in this case is considered for the circulating harmonic current in the neutral. please provide additional details regarding the load and the source.

Thanking you

The panel is serving a data center with a lot of non linear loads. they told me they didn't need the 200% because the currents will cancel each other out on the neutral bus at the panel. My point is these are nonlinear so they won't cancel out like a typical circuit.

Dear Forum member,

your are right. the harmonic current doesn't cancel out. the harmonic current flows though the neutral which causes overheating of the busbar. that is the actual reason why the neutral conductor is sized double that of phase conductor. there is a similar thread in this forum which will give you the detailed answer. just search the keyword 200% neutral. you will find a detailed answer, i think by Mr. Msmad.

Thanking you