Switchgear Estimation Explained: MCCB, ACB, Contactor and Relay Costing Done Right
Switchgear is 55 to 65% of an LT panel’s cost. Get it right and everything else is a rounding adjustment. Get it wrong and no amount of discipline on labour hours or sheet metal will save the job.
Yet switchgear costing is routinely treated as a lookup exercise — find the rating in the price list, apply a discount, move on. That approach misses most of what determines the price.
The problem: the rating isn’t the price driver
Two panels both need “a 250A 4-pole MCCB.” Depending on four other attributes, the price difference between them can exceed 100%.
Breaking capacity. A 250A MCCB at 25kA and the same frame at 50kA are different products at meaningfully different prices. The specification’s fault level — not the current rating — determines which one you’re allowed to quote.
Release type. Thermal-magnetic versus microprocessor-based electronic release. The electronic version costs substantially more and is mandatory whenever the specification asks for adjustable LSIG protection or communication.
Frame size. Manufacturers group ratings into frames. A 250A breaker at the top of a 250A frame and a 250A breaker at the bottom of a 400A frame are priced very differently. Specifications sometimes force the larger frame for future upgrade capability.
Accessories. Shunt trip, undervoltage release, auxiliary contacts, rotary handles, interlocks. Separately priced, 8 to 15% of breaker cost, and invisible on the single line diagram.
An estimator who reads only “250A 4P” from the drawing is guessing on four dimensions at once.
The pain: how this actually plays out
The under-quoted breaking capacity. The SLD shows 250A. The estimator prices a 25kA device because that’s the standard stock item. The specification, three pages in, states a 50kA system fault level. The client’s technical review catches it, and you either absorb the difference or explain to a procurement manager why your quotation didn’t meet spec. Neither conversation is good.
The missing accessory sheet. Nine MCCB feeders, each needing an extended rotary handle with door interlock, none of them on the drawing. At real prices this is a five-figure omission on a mid-size panel, discovered at the purchase stage.
The stale list price. Manufacturers revise pricing several times a year. Quoting from a four-month-old file on 60% of your panel cost is a silent, systematic margin leak — and because it applies uniformly to every quote, it never shows up as an anomaly.
The discount that lives in someone’s head. Your discount varies by brand, product family and volume. If it isn’t recorded, two estimators apply different numbers to the same item and your pricing becomes a matter of opinion.
What you need to identify before pricing anything
For air circuit breakers (ACB):
- Current rating and frame size
- Number of poles (3P or 4P — 4P is significantly more)
- Breaking capacity (Icu and Ics — Ics = 100% Icu costs more than Ics = 50% Icu)
- Fixed or draw-out execution (draw-out is a large premium)
- Manual, motorised (MDO) or electrically operated (EDO)
- Release type — microprocessor with LSIG, and whether earth fault protection and communication are required
Accessories: shunt trip, undervoltage release, spring charging motor, auxiliary contacts, mechanical interlock, door interlock, safety shutters
For moulded case circuit breakers (MCCB):
- Rating, poles, frame size
- Breaking capacity per the system fault level
- Thermal-magnetic or electronic release; fixed or adjustable
- Accessories: rotary handle with door interlock, shunt trip, auxiliary and alarm contacts, terminal shrouds
- Terminal type — front, rear or extended
For contactors and overload relays:
- AC-1 versus AC-3 duty (AC-3 for motor loads; the same physical contactor is rated lower for AC-3)
- Motor kW rating and starting method — DOL, star-delta, soft starter or VFD
- Coil voltage
- Overload relay type — thermal bimetallic or electronic — and setting range
- Auxiliary contact blocks
For protection relays:
- Electromechanical, static or numerical
- Protection functions required (ANSI codes — 50/51, 50N/51N, 27, 59, 87)
- Communication protocol if specified — Modbus, IEC 61850
The gap between a basic overcurrent relay and a numerical multifunction relay with 61850 is the single widest price range in the panel
For current transformers:
- Ratio, class (0.5 for metering, 5P10/5P20 for protection), burden in VA
- Resin cast or tape wound
Class 0.5 metering CTs cost noticeably more than protection CTs, and specifications frequently require both on the same feeder
Six selection decisions that change the price bracket
1. Icu versus Ics. Ultimate breaking capacity versus service breaking capacity. A device with Ics = 100% Icu can be put back into service after a full fault interruption. Many specifications require it. Many estimators don’t check.
2. Cascading and coordination. Correctly applied cascading lets a downstream device with lower standalone breaking capacity be used behind an upstream device — legitimately, per the manufacturer’s tested tables. It can reduce cost significantly. It also has to be documented and defensible.
3. Discrimination requirements. If the specification demands full selectivity between incomer and outgoing feeders, you may be forced into electronic releases with adjustable time delays where thermal-magnetic would otherwise have sufficed.
4. Ambient derating. Panels in hot environments or with poor ventilation require derating. A breaker sized for 40°C may need the next frame up at 50°C, which changes both the price and the panel dimensions.
5. Approved makes. When the client mandates a specific make, your negotiating position with that brand’s dealer determines your margin. When multiple makes are approved, choose the one where your discount structure is strongest — this is a commercial decision estimators often don’t realise they’re allowed to make.
6. Type-tested assembly requirements. If the specification calls for a type-tested assembly, your component choices may be constrained to the combinations covered by the manufacturer’s test certificate. This is a compliance issue that quietly becomes a cost issue.
The pricing discipline that actually matters
Store list price and discount separately. Every switchgear line should carry three numbers: current list price, applicable discount, resulting net rate. Storing only the net rate means you can’t tell whether a change came from a price revision or a discount change — and you can’t re-price a historical quotation.
Date every price. A price without a date is a guess with confidence attached. Treat anything older than 30 days as needing verification.
Discount by brand and family, not globally. One global discount field guarantees you’re mispricing most items.
Reference, don’t embed. BOM rows should point at a price library, not contain typed rates. This is what makes a price revision propagate across every open quotation instead of requiring 40 spreadsheets to be reopened.
Track escalation separately from margin. A 2 to 3% escalation contingency covers price movement during the quotation validity period. Burying it in margin means you can’t see whether you’re actually making money or just covering drift.
Why this is hard to maintain by hand
Four or five manufacturers, each with several product families, each revising list prices on their own schedule, each with a different discount structure that depends on your annual volume — that’s a maintenance job, not a spreadsheet.
Most shops handle it by having one person who “knows the prices.” That works until the day it doesn’t, and it means your pricing accuracy is capped by one person’s available attention.
How Switchonomy handles switchgear costing
The price library holds 12,000+ switchgear items across major makes, maintained rather than populated once at launch. Discount structures are configured per brand and product family, with list price, discount and net rate visible on every line so an estimator can see exactly how a number was arrived at.
When the AI extracts a feeder from your single line diagram, it captures rating, poles and breaking capacity, and the accessory lines — rotary handles, shunt trips, auxiliary contacts, CT shorting terminals — are added by rule rather than depending on someone remembering them.
The engineering decisions above are still yours. Icu versus Ics, cascading, derating, which approved make to propose — those are judgement calls, and they should be. What the software removes is the lookup, the transcription and the risk that your price file is four months old.
See how the price library works with a drawing you’ve already quoted.