How does contact resistance in a relay affect load current and voltage drop?

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Multiple Choice

How does contact resistance in a relay affect load current and voltage drop?

When a relay closes, the contact resistance adds a small but real resistance in series with the load. This means the current through the load is determined by the total circuit resistance: I = V_supply / (R_load + R_contact). If the contact resistance increases, the total resistance goes up, so the load current drops. The voltage across the load is V_load = V_supply − I·R_contact. As R_contact grows, a larger portion of the supply voltage is dropped across the contacts, leaving less voltage for the load. This reduced voltage causes the load current to fall still further, and it can prevent the load from operating properly. At the same time, the power dissipated in the contacts is P_contact = I^2·R_contact. Higher contact resistance means more heat for a given current, which accelerates wear, can cause aging or erosion of the contacts, and increases the risk of contact failure. So, higher contact resistance leads to greater voltage drop and heat, reducing load current and potentially causing wear or failure.

When a relay closes, the contact resistance adds a small but real resistance in series with the load. This means the current through the load is determined by the total circuit resistance: I = V_supply / (R_load + R_contact). If the contact resistance increases, the total resistance goes up, so the load current drops.

The voltage across the load is V_load = V_supply − I·R_contact. As R_contact grows, a larger portion of the supply voltage is dropped across the contacts, leaving less voltage for the load. This reduced voltage causes the load current to fall still further, and it can prevent the load from operating properly.

At the same time, the power dissipated in the contacts is P_contact = I^2·R_contact. Higher contact resistance means more heat for a given current, which accelerates wear, can cause aging or erosion of the contacts, and increases the risk of contact failure.

So, higher contact resistance leads to greater voltage drop and heat, reducing load current and potentially causing wear or failure.

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