If that voltage is not the same it will trip gfci.
Neutral wire bus bar.
When there is two neutral wires in one hole on the neutral bar of an electrical panel several things may happen.
There is nothing neutral about a neutral wire.
It is a current carrying conductor just like a hot wire and has all the potential for danger and should be treated with the same respect.
The original bar is mounted in a plastic housing which i assume isolates it from the box.
There is also a bare ground wire from the neutral bar to the water pipes.
You can see this clearly in the picture below as there are multiple neutral wires feeding into a single screw in more than one instance in this spaghetti mess of wires.
They relate to safety and should be corrected.
And on spas if ground wire is loose or water filled equipment you can have that voltage in water.
The black hot wires are protected from overload by circuit breakers in the panel which typically sense the current in the hot wire and trip out if current is exceeded for too long.
The problem primarily comes from the inappropriately named neutral wire.
The bare wire is a ground to.
Gfci s work differently and can put out a voltage on the neutral to be reconciled later on the ground bus.
Your answer is yes you do put in the bare wire with the white wire.
The main feed is 3 wire with 2 hot legs to the main breaker and an aluminum wire to the neutral.
Consider the schematic for a flash light.
Neutral bars are widely used in residential and commercial electrical service panels to terminate all those white neutral or return wires from the many load circuits in the building.
Some gfci breakers have between 30 80volts on neutral.
Neutral bus bar once the power leaves the electrical service panel through the hot wire s of a circuit and does its work through the electrical devices light bulbs outlets etc the electrical current returns back to the service panel through the neutral usually white circuit wire which is connected to the neutral bus bar.
Information about what is a neutral bar and how it useful in service panels.