Two battery switches can have similar housings and current descriptions while connecting entirely different circuits. Before comparing quotations, define which battery must supply which load group in every required position. Then compare the proposed switch's documented terminal connections with that requirement.
A selector chooses a supply path; a dual circuit arrangement can control two separate paths together. A combine feature adds another connection state. These descriptions must be checked against the exact model diagram, including any external charging connections.
This guide addresses circuit function and purchasing evidence. Use the battery disconnect specification guide for the broader specification package. A connection-state review is not an installation design or permission to operate a switch under load.
Start with named batteries and load groups
Give each battery bank and load group a stable identifier, such as B1, B2, L1 and L2. Record what each identifier means on the project drawing. Do not use an unlabeled sketch of two batteries as a substitute for a circuit requirement.
State whether normal operation requires both load groups to run independently, all loads to use one selected bank, or another arrangement. Identify whether a temporary combined-bank mode is required, prohibited or subject to separate design approval.
Keep electrical connections and user-facing labels linked. A drawing may name terminals A and B while the front panel says START and HOUSE. The RFQ should include the mapping between them and the viewing direction used to identify the terminals.
Also identify any loads connected outside the proposed switch and every charging source. The scope of an OFF position cannot be assessed from the switch alone if another path remains connected to the same equipment.
Distinguish selection from simultaneous circuit control
Blue Sea Systems describes its 9001e as a four-position selector that routes battery banks to the loads or combines the banks to those loads. Its product page separately identifies the selector function, number of positions and combine feature. This is a named manufacturer example, not a specification for every product called a battery selector. Blue Sea 9001e selector data.
For a quotation using a common-output selector arrangement, ask the bidder to show which bank reaches that output in each position. Connecting two load groups to one common output does not, by itself, create two independently supplied circuits. The relevant evidence is the proposed schematic, not the number of cables visible in a photograph.
Blue Sea's 5511e instead identifies a Dual Circuit Plus function: two isolated battery paths can be controlled together, with a separate combine function. The manufacturer also warns that the combine feature prevents using that product to switch positive and negative conductors as separate poles. Do not generalize a dual circuit label into permission for that application. Blue Sea 5511e function and restrictions.
Require the offered part's own terminal diagram and restrictions. A similar-looking switch, or a version without a combine function, may require a different circuit review even when its mounting dimensions match.
Ask for a connection-state matrix
A connection-state matrix lists the intended electrical relationships for each position. Pair it with the actual terminal diagram. The matrix should identify connected paths, paths that must remain separate and exceptions caused by equipment outside the switch.
Blue Sea's two-bank Dual Circuit Plus example describes ON with the house bank feeding house loads and the start bank feeding the engine circuit separately. Its COMBINE state joins both banks and both load groups. These notes explain that particular arrangement; they are not a universal wiring plan. Manufacturer two-bank operating example.
Use the following worksheet to request project-specific evidence rather than copying a generic state table into a purchase order.
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| RFQ question | Required supplier response | Comparison check |
|---|---|---|
| What is connected in each position? | Terminal-to-terminal state table and matching diagram | Every named battery and load path is accounted for |
| What remains separate during normal operation? | Explicit statement of required open paths | No undocumented common output or internal link |
| What does a combine position connect? | Full set of connected terminals and applicable restrictions | Compare against the approved combine-mode requirement |
| What happens outside the switch? | Charging, bypass and unswitched paths identified on the system drawing | OFF and normal-state claims have a defined scope |
| What happens between positions? | Manufacturer's transition description and operating limitations | No inference from steady positions alone |
| How will the supplied part be identified? | Part number, diagram revision and panel legend | Samples and production records refer to the same configuration |
Do not leave an empty cell to mean both “disconnected” and “not yet confirmed.” Mark unanswered relationships as unresolved. Record an explicit supplier response before approving the functional specification.
Keep charging control separate from the handle position
An automatic charging relay, or ACR, is a separate device with its own operating conditions. Blue Sea's Add-A-Battery documentation identifies both a manual switch and an ACR in the kit. Its FAQ explains that the ACR responds to bank voltage and does not direct charging preferentially to the bank with the greatest need. That distinction matters when comparing a switch-only offer with a switching-and-charging package. Blue Sea Add-A-Battery components and FAQ.
Ask the designer to account for the actual alternator, charger, solar controller, relay or DC-to-DC equipment in the proposed system. A switch quotation should identify whether such equipment is included, excluded or only shown as an interface. Do not assume a manual combine position provides automatic charging management.
Where automatic equipment can create another connection between banks, define which device states the system review covers. A matrix describing only the manual switch's internal contacts cannot establish the whole system's connection state in every charging condition.
Battery chemistry, bank voltage and manufacturer restrictions require their own compatibility review before any combined operation is accepted. A product's combine label is not evidence that arbitrary battery banks may be connected together.
Compare a fictional switch quotation
Consider project S-037, an invented procurement exercise. Its approved functional requirement calls for B1 to supply L1 and B2 to supply L2 separately in NORMAL, with both switched supply paths disconnected in OFF. The project does not permit a user-accessible combine mode. These are fictional requirements, not recommended settings for a real vessel or vehicle.
Offer A supplies a selector diagram with B1 and B2 feeding one common output. The quotation proposes attaching both load groups to that output. This does not meet the requested separate NORMAL paths. Matching enclosure dimensions or a larger current rating cannot resolve the functional mismatch.
Offer B supplies two separate switched paths and a state table matching NORMAL and OFF, but the offered handle also has a combine position. Its normal-state behavior is closer to the requirement; the additional accessible mode still conflicts with the project specification. Ask for a suitable alternative or a formally approved design change, not an informal instruction to ignore the position.
Offer C identifies two paths without a combine mode and supplies the required table. However, the project drawing also includes an external charging link whose behavior has not been reviewed. The switch function can be recorded as matching the stated internal-contact requirement while system approval remains open pending that review.
This comparison separates a definite mismatch from missing system evidence. Record both clearly so procurement does not treat the most complete-looking quotation as an approved installation.
Close the evidence package before release
Review steady positions and transitions separately. Terms such as make-before-break describe contact sequencing within the manufacturer's stated scope. They do not replace operating restrictions, switch ratings or the charging equipment's instructions. Ask for those documents rather than inferring permissible live operation from a marketing phrase.
Specify how sample identity and contact-state evidence will be recorded under an agreed, appropriately controlled inspection procedure. Do not improvise a test on a live battery system to settle a quotation question. A functional inspection record also does not establish endurance, voltage suitability or cranking capability; see the switch duty and repeated-starts guide for separate evidence requirements.
Submit the state matrix, system diagram, terminal mapping, required legend, quantities and requested records together. Ask bidders to separate the switch, charging accessories, panel labeling and sample evaluation in their commercial scope. Follow the first-article and change-control approach when a later switch variant or drawing revision changes an accepted connection.
Buyer FAQ
Are a two-battery selector and a dual circuit switch interchangeable?
Not automatically. Compare every terminal connection and required position against the project matrix. Similar size, terminal count or current descriptions do not prove equivalent functions.
Does OFF prove the entire installation has no power?
No. Its meaning depends on the switch connections and any external paths. System isolation requires the applicable design and procedure; a handle label alone does not establish it.
Does a combine position replace an automatic charging relay?
No. Manual contact selection and automatic charging-related control have different roles. Identify the required function and the exact equipment providing it in the proposed system.
What should suppliers include to make quotations comparable?
An exact switch part, controlled terminal diagram, connection-state matrix, restrictions, accessory scope and sample evidence plan. Request current price and delivery terms for that defined configuration.