Follow up questions regarding my NAD C375BEE

I'm not positive the NAD uses a 3 lug connector (some NAD amps don't) but if it does, use the cheater as Rar1 suggests and see if the hum goes away.
If the NAD does not use a 3 prong connector, use the cheater at the sub power cord.
Another trick is to use a small gauge wire connected from the chassis of the NAD to the sub amp chassis. It may have a ground lug on the sub-not sure as I'm not familiar with this brand. Worth a try.
As for your amp going out on protection, is it both channels or one channel? If both, I would suspect something in the power supply of the amp. This would require a visit to the shop for correction.

It would seem to me that you have two issues here; perhaps they are related, but it is also quite possible that they are not related. The first thing I would do is isolate the two conditions (protection circuit and hum) by completely removing the sub from the system. Secondly, I wouldn't consider it a forgone conclusion that the amp is damaged just because the protection circuit is activated, especially if you powered off shortly afterwards.

I have the 375 also, and I think it to be a fine amp capable of driving just about any speaker. I find it puzzling that some would suggest it isn't robust enough. That just doesn't seem to be a rational suggestion; clearly information is missing somewhere.

When the sub is completely disconnected from the amp (all wires and interconnects removed), is the protection circuit still activating? If so, the next item to examine is the connections to the speakers. The 375 has two sets of speaker posts (A and B). Are you using only one set (A or B) of speaker posts or are you using both speaker posts (A and B)? If using both, what speakers are the second set of posts connected to?

On the back of the amp, I prefer the soft clipping be turned off but this is just a matter of preference. Also, the amp should be set to stereo. One more idea: there is a fuse with access from the back of the amp. You may want to pull the fuse out and take a peek at it. Perhaps the fuse is blown. Keep in mind a blown fuse is a symptom, not the cause. You will still need to trouble shoot to determine what caused the fuse to blow.

If the protection circuit is not activated when the sub is completely disconnected, then there is a problem with the way the sub is hooked up and connected to the amp.

We can give more specific help once we have a better idea how the amp performs independently and without any sub connected.

Pgawan2b, I do think you are offering good advice, however, the part about looking at the fuse makes no sense. That is an AC power fuse, so if it is blown, the unit will be totally dead and not work. The unit works, but with the protection circuit activating prematurely.

Update:
It looks like the OP started a thread at Audioholics at the same time, it's about the NAD C375, Totem Ones as well with the NAD protection circuit activating too. Later on in that thread, he adds that his previous integrated, an Anthem 225, had issues too. One speaker was much quieter so he had to adjust the balance knob and decided the Anthem was going and bought the NAD.

Now the NAD needs the balance adjusted too, but it's shutting down as well. Anyway, it's all there in the thread, 2 capable guys are helping him and they think the Totem ones or the sub is damaged.

Tls49, good point and thanks for the correction.