Crane Scale Overload Alarm and Remote Alerts: Stopping the Lift Before the Snap

The scale knows it is overloaded before the wire rope does.

A hoisting rope is built to carry five times the crane’s rated load before it breaks. The number on the hook stops far earlier: by law, no digital scale may show a weight beyond its capacity plus nine divisions. That gap is the whole point of a crane scale overload alarm — the instrument sees the overload while the rope, the hook and the roof beam are still a long way from finding out. This article covers where the display stops, what the alarm can switch (a hooter, a beacon, the hoist, a phone), what the rules ask for, and how to trial one on one crane in thirty days.

The numbers stop before the rope does

Every digital weighing instrument has a legal ceiling on what it may display. The international recommendation for weighing instruments, OIML R 76-1, puts it in one line: there shall be no indication above Max + 9e — the capacity plus nine divisions. India’s Legal Metrology (General) Rules, 2011 carry the identical words, and the US NIST Handbook 44 (2026 edition) allows nothing above 105 % of capacity.

Take a generic 5,000 kg crane scale reading in 2 kg steps. It must stop showing numbers at 5,018 kg. The “OL” legend is the industry convention, and it is how Hindustan Scale Company’s crane scales say it. The law does not require an OL symbol; it requires that the numbers stop, and OL is the scale saying so.

That cut-off is the earliest overload signal a crane scale gives. But it lives on the hook, where the rigger is watching the load, not the display. The rest of this article is about carrying that signal to those who can act on it.

What does a crane scale overload alarm actually do?

It compares the live weight against a threshold and switches something when it is crossed. On an HSCo crane scale the threshold is a setting the customer chooses — usually the crane’s marked safe working load (SWL) — and the outputs stack in four layers.

Layer	What happens	Who it reaches	Which rule describes it
1. Display cut-off	Numbers stop above Max + 9e; the display shows OL	The rigger at the hook	OIML R 76-1; Legal Metrology Rules 2011
2. Local warning	A relay drives a hooter or beacon on the crane or girder	Everyone in the bay	IS 13367-1: visual on approach, continuous audible once exceeded
3. Motion cut-out	The relay, wired into the hoist control circuit, stops hoisting until the load is reduced	The crane itself	IS 3177: “an additional overload safety device”
4. Remote alert	Reading and alarm reach a phone or desk indicator away from the load	The supervisor off the floor	No standard asks for it — an extra layer

Layers 2 and 3 use the HSCo relay add-on: a dry-contact output that can be fitted to the scale and wired to a hooter, a beacon or the hoist contactor. Layer 4 is what the Bluetooth crane scales and the HSCo Android app are designed to do: the weight and the overload event on a phone in a supervisor’s pocket, not on a display above a swinging load.

The margins are not spare capacity

A crane does not fall down at 101 % of its rated load — which is exactly why the margins are dangerous to think about.

A hoisting wire rope is sized so that the rated load is at most one-fifth of its breaking strength — US OSHA caps it at 20 % of breaking strength per part of rope; the EU Machinery Directive sets a working coefficient for ropes that “as a general rule … is equal to 5” (4 for chains). That factor exists for shock loading, wear, corrosion and fatigue over the rope’s life — not for a heavier lift today.

The only overload the law contemplates is a supervised test. OSHA caps the rated-load test at 125 %; IS 3938:1983 and IS 3177:1999 test hoists and cranes at the same 125 %; and India’s Factories Act 1948, now carried under the OSH Code 2020, says no crane, chain, rope or tackle shall be loaded beyond its plainly marked SWL “except for the purpose of test”. Even that test can buckle a structure without warning, IS 13367-1 cautions.

So an overload alarm set at the SWL is not being cautious. It is protecting a margin that was never yours.

What the law asks for — and which device answers it

India. The Factories Act 1948 rule, now carried under the Occupational Safety, Health and Working Conditions Code 2020, sets two duties for every lifting machine: the SWL plainly marked and never exceeded except for a test, and a thorough examination by a competent person at least once in twelve months. IS 3177:1999 recommends load-indicating and load-limiting devices wherever the weights to be lifted are not accurately known; they must sense the load itself and stop hoisting above the SWL. IS 13367-1:1992 defines the automatic safe load indicator as two-stage: a visual warning as the load approaches the SWL, then a continuous audible warning to the driver and to people nearby once it is exceeded.

Europe and the UK. The Machinery Directive requires every lifting machine of 1,000 kg or more (or 40,000 Nm of overturning moment) to carry devices that warn the driver and prevent dangerous movements when overloaded; the EU Machinery Regulation 2023/1230 repeats the clause word for word and applies from 20/01/2027. The UK’s HSE guidance L113 asks for rated-capacity indicators and limiters with audible and/or visual warning, and warns that a failed indicator lets an overload go undetected.

The pattern is plain: a local warning and a motion cut-out, sensed from the real load. The crane’s own limiter meets that; a hook scale with a relay adds a second sensing path that already knows the number to the kilogram.

The load is what kills

The US Bureau of Labor Statistics counted 297 crane-related deaths in 2011–2017, about 42 a year. Just over half were workers struck by an object, and in 79 of the 154 struck-by cases the object had fallen from the crane. Peer-reviewed studies in the Journal of Construction Engineering and Management (2006) and Construction Economics and Building (2015) put “struck by the load” first, at 32 % and 45 % of crane deaths. None of these datasets isolates overload as a cause; what they show is that the falling load is the leading killer, and overload is one recognised way a load falls.

One case shows how. On 21/05/2009, at a Cheshire motor-component maker, a 31-tonne load was lifted on a 27-tonne overhead crane using chains rated for 17 tonnes. The chains gave way, part of the crane was torn from its roof mountings and fell nearly five metres, and the hook shattered a worker’s thigh. The company was fined £20,000 plus £8,792 costs on 31/03/2011; the UK Health and Safety Executive’s inspector said it “regularly expected its workers to lift loads well over the lifting capacities of both the chains and the overhead crane”.

What would a hook scale have done there? A 31,000 kg load on a 27-tonne-class scale would have shown OL, not a number — but it would have said nothing about the chains, rated for barely half the load. Knowing the weight is the first step; marked, rated lifting gear is the second.

What a crane scale overload alarm is not

It is not a rated-capacity limiter. The crane’s own limiter makes the crane lawful. The hook scale’s relay is the additional layer IS 3177 describes — a second opinion from the one instrument that reads the load directly.

It is not a phone app. Phone and desk alerts are designed for the supervisor who is not on the floor. The warning the law recognises is the hooter in the bay and the cut-out in the hoist circuit. Add the phone; never subtract the hooter.

It is not a licence to lift more. HSCo’s CRH crane scale is built to take up to 200 % of its capacity without losing accuracy. That is a statement about the instrument’s robustness — what the standards call its maximum safe load, marked “Lim” — and nothing else. The crane, the rope and the slings have no such headroom.

And it is not a fixed percentage. The Indian standards say “approaches” and “exceeds” the SWL without numbers. HSCo’s thresholds are settings, chosen with the customer against the crane’s marked SWL — and, the Indian code of practice recommends, against half the normal SWL of the lifting gear when the load is molten metal or slag.

What changes for you on Monday morning

1. The weight is known before the lift, not argued after it. IS 13367-1 says the weight must be known with reasonable accuracy; the hook scale settles it on the way up.
2. The bay hears the overload. A hooter on the girder reaches the driver, the slinger and anyone walking past.
3. The hoist stops itself. With the relay in the hoist circuit, an overload ends the lift until the load is reduced.
4. The supervisor knows from the office. Every overload event, with its weight and time, is designed to reach a phone or desk indicator — added to the hooter, never in place of it.
5. The twelve-monthly examination has a record to read. Logged overload events are what a competent person asks for.

How to start: one crane, thirty days

1. Pick one crane — the one whose loads are least often known before the lift.
2. Read the marked SWL off the crane and the rating off its slings. If either is missing, that is the first finding.
3. Hang a CRH crane scale with a capacity at or above the crane’s SWL (1,000 kg to 50,000 kg) and set the overload threshold with HSCo against that SWL.
4. Fit the relay add-on and wire it to a hooter on the girder; decide with your electrical team whether it also enters the hoist circuit. Add the Bluetooth readout if the supervisor works away from the bay.
5. Count for thirty days: lifts made, loads unknown before the lift, and overload events — how many, how heavy, which shift.
6. Bring the log to the next thorough examination and decide from the numbers whether the rest of the bay follows.

Hindustan Scale Company has built weighing instruments in Mumbai since 1955. The full crane scale range is on the website; the crane scale buying guide covers capacity, division and display choices.

Frequently asked questions

What is a crane scale overload alarm?

A crane scale overload alarm compares the live weight on the hook with a set threshold — usually the crane’s marked safe working load — and switches an output when it is crossed: a hooter or beacon, a relay into the hoist control circuit, or an alert on a phone or desk indicator. It adds a second load-sensing path to the crane’s own limiter; it does not replace it.

At what weight does a crane scale show OL?

By law a digital scale may show no number above its capacity plus nine divisions (Max + 9e). A 5,000 kg scale reading in 2 kg steps therefore stops at 5,018 kg. What replaces the digits is the maker’s choice; the OL legend is the convention HSCo uses.

Does a crane scale overload alarm make my crane compliant with IS 3177 or the Factories Act?

No. The crane’s own rated-capacity limiter and indicator are what satisfy IS 3177 and IS 13367-1, and the safe-working-load and twelve-monthly examination duties sit with the crane owner under the Factories Act rule now carried by the OSH Code 2020. A hook-scale alarm with a relay is the “additional overload safety device” IS 3177 describes — a useful extra layer, not the compliance device.

Can the overload alarm stop the crane?

It can be wired to. The HSCo relay add-on gives a dry-contact output that a plant electrician can take into the hoist control circuit, so an overload stops further hoisting until the load is reduced — the behaviour IS 3177 clause 11.3 describes for a load-limiting device. Whether it should is a decision for your electrical team and your competent person.

Can I get the overload alert on my phone?

Yes, as an extra layer. HSCo’s Bluetooth crane scales and Android app are designed to put the reading and the overload event on a phone at a safe distance, and a desk indicator can do the same in the office. No standard asks for a phone alert, and it never replaces the hooter and beacon in the bay.

How much does a crane scale with an overload alarm cost in India?

The CRH crane scale is listed at ₹14,500 to ₹26,500 depending on capacity — indicative, before GST — with the relay add-on, the Bluetooth readout and the app priced separately. The exact figure depends on capacity, division and which outputs you need; the configurator on the product page gives the current price.

Next step

Tell us the marked SWL of one crane and what it lifts, and we will propose a thirty-day overload-alarm pilot for it.

Hindustan Scale Company (HSCo) · Mumbai · est. 1955 · www.hindustanscale.com · hsc@hindustanscale.com

Sources

1. OIML R 76-1:2006 — Non-automatic weighing instruments, Part 1: Metrological and technical requirements, clauses 4.2.3 (limits of indication), T.3.1.7 and 7.1.2 (maximum safe load, Lim); OIML R 60 (2000), clause 2.3.15 (safe load limit).
2. Legal Metrology (General) Rules, 2011 (India), Seventh Schedule, Heading A — para 4(2)(iii) limits of indication; terminology 3(1)(vii) maximum safe load.
3. NIST Handbook 44 (2026 edition), Section 2.20 Scales, S.1.7(a) and (b) — capacity indication limits.
4. The Factories Act, 1948 (India), s.29; Occupational Safety, Health and Working Conditions Code, 2020, s.143 (repeal and savings); Press Information Bureau release 2192900 (22/11/2025).
5. IS 3177:1999 (Bureau of Indian Standards) — Code of practice for electric overhead travelling cranes and gantry cranes other than steel work cranes, clauses 11.3, 15.12 and 26.2; IS 3938:1983 — Electric wire rope hoists, clause 21.2.
6. IS 13367 (Part 1):1992 (Bureau of Indian Standards) — Safe use of cranes: code of practice, Part 1 General, clauses 3.2, 9.9, 13.1, 14.2.2, 17.1.1 and 17.3.
7. Directive 2006/42/EC on machinery, Annex I, 4.1.2.4 and 4.2.2; Regulation (EU) 2023/1230 on machinery, Annex III 4.2.2, Articles 51(2) and 54 (as corrected, 2024).
8. HSE (UK) — L113 Safe use of lifting equipment, LOLER 1998 Approved Code of Practice and guidance, 2nd edition (2014), paras 117, 188–191, 262, 282–284 and 327.
9. US OSHA — 29 CFR 1910.179 Overhead and gantry cranes, paras (b)(5), (h)(2)(i), (j)(1)(ii), (k)(2) and (n)(1).
10. US Bureau of Labor Statistics — Fatal occupational injuries involving cranes, 2011–17 (Census of Fatal Occupational Injuries fact sheet, May 2019).
11. Beavers J. E., Moore J. R., Rinehart R., Schriver W. R. — “Crane-Related Fatalities in the Construction Industry”, Journal of Construction Engineering and Management 132(9), 2006; Gharaie E., Lingard H., Cooke T. — “Causes of Fatal Accidents Involving Cranes in the Australian Construction Industry”, Construction Economics and Building 15(2), 2015.
12. UK Health and Safety Executive — press release “Cheshire car parts maker fined over crane injuries” (31/03/2011); The Construction Index — “Load fell because rated capacities were ignored” (01/04/2011).
13. Hindustan Scale Company — CRH Electronic Crane Scale product page (capacities, outputs, overload statement, indicative price range before GST).