Running a master switch to a panel seems strange to me because my heads macerator was run from the same auxiliary battery
that supplied the anchor windlass
. It did however connect to a 30 amp relay which switched on the macerator/pump--so the little flush switch on its neat little box only drew a couple of amps. The 30 amp relay switched the 15 amps the motor drew through its own platinum contacts. In over eight years I replaced the heads once--but never the switching.
I suspect you have an obstruction in the pump--and visitors aboard often have no idea that some items should never be disposed of in a marine head
As for the wiring
of same, why would one run such a long length of 15 amp capable twin wire from the heads to a master panel? It would require at least 6 mm diameter wire to do that--and then probably not well.
There is WAY too much extraneous wire cluttering the average boat. If you must use a master switch to isolate the heads--use a proper isolating switch capable of carrying 100 amps. They cost about fifty bucks. Mount it in the local lead from the master bus-bar to the heads motor directly just besides the operating switch for the flush/macerator..
I only have a few things connected to a master panel. None of them are engine
controls, none of them are essential circuits, (only manual overrides). The two isolating switches for the battery
banks have their position BEFORE any master panels
are involved--and are situated below the master panel. They are only ever used when the vessel is out of the water, or when an auxiliary battery takes over while maintenance
or replacement of batteries
takes place. There are two covered terminals for the connection of such a temporary supply, on the panel side of the master switches, a battery which in my case came in the form of a portable rechargeable engine-start pack. It would run gas detectors and bilge
pumps, water supply, radios and nothing else, for the hour or so I nedded to do any essential maintenance or replacements