# Can an arc happen if only one contact on multiple parallel batteries disconnects?

If there are multiple high voltage batteries in parallel, and one of the contacts is unreliable and disconnects sometimes, does the other contact take away the arcing potential, since it's always on?

The current from the cut contact can travel through the other battery, which has a resistance of i.e. 50 milliohms

If there is current flowing through the contact, there is arcing potential. It is a well known cause of battery explosions when disconnecting batteries. Unless you have a zero-impedance battery bank, and zero-inductance battery connections, sparking will occur.

In practice, charge and discharge currents are large, battery connection paths are inductive, and battery impedance is significant at charge/discharge current levels.

In theory 'both connections' might be at the same voltage, and both sides of the connection might be at the same voltage, but in actual practice this is not effective, and disconnecting half a battery bank can cause sparking, and, for power applications, can actually cause persistent arcing.

Disconnecting half of a battery bank is significantly less dangerous than disconnecting all of a battery bank, or disconnecting the second half of a battery bank. But even when building a double-battery bank, proper connect/disconnect switching should be provided -- protected contacts or DC circuit breaker or switch gear -- so that the current can be zero'd or the arc suppressed.

does the other contact take away the arcing potential

If both batteries have the same terminal voltage then, when the unreliable contact goes open circuit there should, ideally, be no voltage across that broken contact. If both batteries don't have the same terminal voltage then you should never consider paralleling them without very good technical reasons.

In other words, there is no "arcing potential".

I was hoping for a technical explanation discussing the momentary change in resistance and the voltage spike that results in arcing and current inertia. – DwayneDeSouza

From your description, there is no voltage spike and there is no current. Current inertia is something new to me. If you want answers, you have to ask the right question and, from the details in your question, there can be no current and no spark or arc.

If there is (somehow) a current flow, then an arc will happen on the disconnecting contact and not the contact that remains closed. That arc will depend on the amount of current and circuit inductances. But, with two batteries in parallel, there is no current flow between them unless, of course they have non-identical voltages (see part 1 of this answer).

• I was hoping for a technical explanation discussing the momentary change in resistance and the voltage spike that results in arcing and current inertia. Commented Oct 16, 2021 at 11:03
• From your description, there is no voltage spike and there is no current. Current inertia is something new to me. If you want answers, you have to ask the right question and, from the details in your question, there can be no current and no spark or arc. Commented Oct 16, 2021 at 11:06
• See additions to my answer. Commented Oct 16, 2021 at 11:15
• 'current inertia' is generally quantified by the concept of inductance. Commented Oct 17, 2021 at 7:36