DISTRIBUTOR-FIRST SUPPLY PARTNER · SINCE 1999 Live · Electrical & Controls System
SPC Company
Electrical & Controls / Control & Logic / Control & Logic
System · Electrical & Controls Layer 2 · Control & Logic 1 product types

Control & Logic

Lead-lag relay logic that evens run hours and stages paired equipment cleanly.

Request a quote → Compare the 1 types ↓ See the decision guide ↓
The Control & Logic family 1 types · Control & Logic
Alternating Relay

Tap any type to jump to its page. The Decision Guide further down asks three questions that funnel the spec to one of these.

Real-world reference Representative control & logic
Category family Control & Logic
What this category is

The small relay that changes how paired machines age

CONTROL
Logic before load

Control & Logic sits between the pressure signal and the starter, deciding which machine leads and which one joins as demand rises.

RUN HOURS
Alternation prevents one-machine wear

Alternating the lead role helps paired compressors or pumps share starts, run time, and maintenance intervals.

VERIFY VOLTAGE
Match coil and contact ratings

Control voltage, contact rating, and mounting style determine whether a relay belongs in the panel.

The 1 types · side-by-side

Best-for, key trade-off, capacity, price band, and how deep the brand bench runs.

Distributor-facing reading. The trade-off column is the one that closes the loop — every type buys something and gives something up. Knowing what each type costs you is how the right one gets on the quote without a callback.

Product type
Best for
Key trade-off
Typical capacity
Price band
Brands SPC carries
Alternating Relay →
Duplex lead-lag alternation Use when two compressors or pumps need to alternate lead duty and bring on the lag unit only when demand requires it.
Control-only device The relay does not replace the starter, overload, pressure switch, or panel wiring that does the actual switching.
Coil voltage and contact rating matched
$$
2 / 5 ? electrical control item
Decision guide

2 questions “Funnel the Spec” to one product type.

Draw a line from the customer's answer at the top to the type name at the bottom. This is the page distributors screenshot and send to a customer the day before a quote call — so the customer comes prepared with the answers, and the call is about the brand and the budget, not the basics.

Use this Print this page, drop it in an email to the end customer, or screenshot the tree below. The questions and the type recommendations are designed to stand on their own without the rest of the page.
START AT THE TOP  ·  FOLLOW THE PATH DOWN  ·  END ON THE PRODUCT TYPE
Question 1
Is the customer trying to alternate paired equipment?
Yes, two units need lead-lag rotation
Recommend
Alternating Relay
Quote an alternator relay matched to control voltage, contact rating, and mounting style.
See product type →
No, the problem is starting one motor
Recommend
Magnetic Starter
Route single-motor switching back to the starter and overload selection.
See product type →
The inputs behind the tree · what we'll need to quote

4 answers settle the right control & logic — gather these before the quote call.

01
How many units are being alternated?
Duplex and triplex logic require different control layouts.
02
What is the control voltage?
Coil voltage mismatch is the most common wrong-part risk.
03
What loads do the relay contacts switch?
Contact rating must match the circuit it controls.
04
Is this panel mount or DIN rail?
Mounting style determines the relay package.
Where this category lives
L2
Electrical & Controls System · Layer 2

Control & Logic

The relay and sequencing layer that decides which compressor or pump runs first and when the lag unit joins.
→

Control logic protects paired equipment from uneven run hours and helps a compressor room stage demand without relying on manual switching. The quote starts with the number of units, the control voltage, and the lead-lag behavior required.

Categories in this layer
Role in the layer
Power & Drive

Control switches the starter: the logic decides, the starter acts.

→
Role in the layer
Compressor Room

Where the logic earns its keep: duplex and triplex compressor rooms that need lead-lag alternation so run hours stay balanced and the standby unit actually cycles.

→

Not sure which type? Send us the use case.

Tell us the end-use, the rough flow, and what climate the unit would sit in. We'll come back with a configured quote — the right type, the right tier, and the upstream gear the warranty assumes.

Talk to a specialist →