WirthCo Battery Disconnect Switches: Terminal Types & Amp Ratings

WirthCo Battery Doctor disconnect switches are available in several designs, from a blade mounted directly at the battery post to a panel-mounted rotary master. The correct choice depends on the battery terminal, cable connections, continuous current rating and how the switch is intended to isolate the circuit. A switch that looks similar may connect differently.

Start with the battery connection, not the switch shape

Top or side battery post?WirthCo 20138 and 20148 are top-post blade designs. 20128 uses a side-terminal connection; 20307 and 20310 are compact side-post knobs. Check the polarity and battery terminal type before ordering.
Direct mount or remote?20188 is an in-line blade with bolted cable-eyelet connections for a more accessible location. 20304 and the 20387/20393 rotary switches use other mounting arrangements.
What should the switch control?Basic ON/OFF isolation, retained low-current memory power and selecting between two batteries require different functions. Use the exact switch design, not only its amperage.

Understanding continuous, surge and cranking ratings

Continuous current describes what a switch can carry during sustained operation. A separate short-duration surge or starting rating is not a substitute for the continuous rating. Check battery system voltage, connected loads, cabling, protection and the installation instructions for the exact MPN.

250 A knife-blade family

WirthCo's 20128, 20138, 20148 and 20188 knife-blade switches are rated 250 A continuous and 750 A surge at 12V. The difference is how each unit connects to the battery.

125 A compact family

20307, 20309 and 20310 are rated 125 A continuous and 500 A surge at 12V. Only 20309 and 20310 in this group have a 15 A fused bypass.

WirthCo disconnect switch MPN comparison

Compare part numbers by operating method and connection style. The ratings here identify the switch family; they do not establish compatibility with every RV charging system, inverter or starter circuit.

MPN Control Mounting Continuous Distinct feature
20128 Knife blade Negative side-terminal battery 250 A Side-terminal mounting; eyelet cable connection
20138 Vertical knife blade Negative top-post battery 250 A Top-post style with vertical operation
20148 Vertical blade with wing nut Negative top-post battery 250 A Additional wing-nut stud connection
20188 Knife blade Remote in-line cable position 250 A Two bolted eyelet-cable terminals
20304 Lever / rotary master switch In-line panel opening 100 A at 12 V Requires ¾-in panel mounting hole
20307 Compact removable knob Negative side-terminal battery 125 A at 12 V No fused bypass
20309 Compact removable knob Negative top-post battery 125 A at 12 V 15 A fused bypass for low-current memory loads
20310 Compact removable knob Negative side-terminal battery 125 A at 12 V 15 A fused bypass for low-current memory loads
20387 Two-position ON/OFF rotary Surface or panel mounting 300 A Single-circuit master; removable rear cover
20393 Four-position battery selector Surface or panel mounting 300 A OFF / 1 / BOTH / 2 battery selection
Fused-bypass safety: WirthCo 20309 and 20310 include a 15 A fused path intended to retain small memory loads when the main battery connection is switched off. This means the downstream circuit is not completely de-energized. Do not rely on a bypass-style switch as the sole electrical isolation for service work.

Shop WirthCo battery switches by connection style

These links open the individual products in our catalog. Match the exact manufacturer number and mounting arrangement before choosing a replacement.

Knife-blade disconnects

These 12V knife-blade disconnects are rated 250 A continuous, 750 A surge. Pick the terminal and cable connection arrangement that actually matches your battery.

Compact knobs and in-line lever

A removable-knob switch and a lever-operated master are not the same assembly. Verify 100 A versus 125 A continuous ratings, side or top posts, and any fused bypass.

WirthCo Battery Doctor 20309 Compact removable knob product listing image

WirthCo 20309

125 A at 12 V continuous

Compact removable knob

15 A fused bypass for low-current memory loads · View details

WirthCo Battery Doctor 20310 Compact removable knob product listing image

WirthCo 20310

125 A at 12 V continuous

Compact removable knob

15 A fused bypass for low-current memory loads · View details

Rotary master switches

20387 provides ON/OFF operation; 20393 adds OFF/1/BOTH/2 selection for a different battery architecture. Both are listed at 300 A continuous.

Common battery-switch questions

What is the difference between WirthCo 20309 and 20310?

Both are 125 A compact switches with a 15 A fused bypass. 20309 attaches to a negative top battery post, whereas 20310 is for the negative side post.

Can I replace WirthCo 20387 with 20393?

They use different switching functions. 20387 is an ON/OFF master, while 20393 is a four-position battery selector with OFF, battery 1, BOTH and battery 2 options. Replacing one with the other may require a different circuit layout.

Is a 250 A surge rating enough for a 250 A continuous load?

No. Surge and continuous ratings describe different durations. Choose the switch using its manufacturer continuous rating, the actual circuit duty and the electrical system's protection requirements.

For the role of fuses, switches and inverter protection in an RV system, see our RV battery distribution reference. Two-battery systems also have different selector choices: compare the Blue Sea dual-circuit switch guide and BEP switch comparison.

Manufacturer resources: WirthCo knife-blade switch family, 20309 fused-bypass specifications, and Battery Doctor manufacturer catalog (PDF). Work on battery circuits should follow the exact manufacturer's instructions and appropriate protection procedures.

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