NFPA 110 Battery Charger Requirements for Specifiers
NFPA 110 battery charger requirements sit in Chapter 5 of the standard, in the starting-equipment provisions at §5.6, and they cover four things: that the charger works automatically, that it can restore a discharged battery, that its performance can be observed, and that failures are annunciated. Everything else in a charger specification is either a detail of those four or a decision the project makes for itself.
The part that catches projects isn’t the list. It’s that the numbers attached to those requirements move between editions, and a specification written from a remembered figure can be wrong before the tender closes.
This article is written for the person who has to put the requirement into a document and defend it: what the standard asks for, how each requirement becomes a line in a specification, and how to confirm the specifics against the edition your project is actually governed by. If you are looking for the wider compliance picture rather than the charger clauses, our NFPA 110 compliance guide covers the classification system and testing regime.
At ZC Power we build generator sets from 8 kVA to 4000 kVA and supply the charging arrangements that go with them, so we spend a lot of time reading charger clauses as they arrive in customer specifications. The failures we see are rarely dramatic. They are usually a clause carried forward from an older project, or a charger bought to a rating that no longer matches the battery.
Key Takeaways
- The charger requirements are in NFPA 110 Chapter 5, in the starting-equipment provisions at §5.6, that’s the part to cite when a supplier asks what you are specifying against.
- The system Level drives the requirement. A Level 1 system carries a stricter recharge obligation than a Level 2 system, so the Level is decided before the charger is.
- The recharge window is a sizing input, not a label. It sets the minimum charger current once you know the battery capacity and the standing DC load.
- Settle whether the charger or the controller carries the alarms. These are different requirements and specifications routinely conflate them.
- Verify the edition-specific figures before you publish a tender. A number carried forward from memory is the most common defect in this clause.
What NFPA 110 Requires of a Battery Charger
NFPA 110 is the standard for emergency and standby power systems. Its requirements for the energy source, the batteries, the charger and the accessories sit in Chapter 5, and the starting-equipment provisions that govern the charger are at §5.6. That is the part to cite when a supplier asks what you are specifying against.
A national-laboratory engineering standard that specifies this equipment requires an automatic battery charger meeting EGSA 100C and references the standard’s starting-system provisions, which is a useful cross-check on the section group even though it is not a substitute for reading the clause.
A note on what follows. What is set out here is a paraphrase of what the requirement covers, not the text of the standard. NFPA 110 is a purchased document, its wording changes between editions, and any figure you put in a tender should be read from the edition your project is governed by. Where this article gives a number, it says whether that number is clause text or common specification practice.
The requirements resolve into four questions a specification has to answer.
- Does it operate automatically? In practice, that means a charger that works without an operator deciding to connect it. On an unattended standby set, anything that depends on a person noticing a flat battery isn’t compliant in intent.
- Can it restore a discharged battery? Not merely hold a charged one. The requirement is about recovery within a defined period, which is why the charger has to be sized rather than selected.
- Can its behaviour be observed? Metering so that charging current and battery voltage can be read without test equipment. This is what makes an inspection possible at all.
- Are failures annunciated? A charger that fails silently is the failure mode the standard exists to prevent.
A charger should also be specified against a performance standard, not just a current rating. The trade standard for this equipment is EGSA 100C, Performance Standard for Battery Chargers for Engine Starting Batteries and Control Batteries (Constant Potential Static Type), and the companion EGSA 100B covers the cranking batteries themselves. Naming those standards in a specification gives a supplier something checkable to certify against, which a bare amperage figure does not.
This is an illustrative composite rather than a record of a specific client. A consultant preparing a tender for a small hospital carried the charger clause forward from a previous project without re-checking it. The clause specified a charger sized to the old battery capacity.
The new project used a larger battery, and the charger quoted to the clause could not meet the recharge obligation on paper. The supplier quoted compliant equipment, the schedule held, and the error surfaced only at commissioning, when the recharge test ran long. Re-deriving the requirement took an afternoon. Discovering it late took a fortnight.
Level 1 and Level 2 Drive the Requirement
NFPA 110 classifies a system by Level, and the Level is assigned from the consequence of failure. Level 1 applies where a failure could cause loss of life or serious injury. Level 2 applies to systems that are less critical to life safety.
The classification isn’t decoration. It’s the variable that sets how strict the charger obligation is, because the recharge window is expressed differently for each Level. That’s why the Level is decided at the system level and inherited by the charger, not the other way round.
Two other classifications sit alongside and are worth keeping straight when you write a specification:
- Type governs how quickly the load must be transferred, in seconds.
- Class governs how long the system must run without refuelling, in hours.
The Level, Type and Class together are what a supplier needs to read your requirement correctly. Our guide to NFPA 110 Type 10 versus Type 60 works through the transfer-time side of that, and it’s worth reading before you write the classification line into a tender.
If you are unsure which classification your project falls into, say so before the charger clause is written. Contact our engineering team with the load description and the building’s life-safety role, and we will tell you what a supplier will expect to see.
The Recharge Window Is a Sizing Input
The requirement to restore a discharged battery within a defined period is the most useful line in the section, because it converts directly into a number.
The arithmetic is straightforward once you have three inputs: the battery capacity in amp-hours, the recharge window in hours, and the standing DC load that the charger must carry at the same time. The charger current has to cover the recharge and the load together, or it will never finish either job.
The figures commonly applied in project specifications are 24 hours for Level 1 and 36 hours for Level 2. They are widely used and they are what most charger sizing is built on. They are also the figures most worth confirming against the edition in force for your project, because a specification that states the wrong window will produce a charger that passes paper review and fails at commissioning.
The full sizing arithmetic, including the DC auxiliary load and the charger’s input demand, is in our guide to sizing a battery charger for a generator. What matters here is the ordering: the window is set by the classification your project is governed by, and only then does the charger current follow from the window.
The monitoring arrangements that let you observe the charger’s behaviour are covered in IEEE work on lead-acid battery monitoring and charging for backup generators.
Charger Alarms and Controller Annunciation Are Not the Same Requirement
This is the clause that most often goes wrong in a specification, and it goes wrong quietly.
There are two different things a project may mean by “alarms”:
- The controller annunciates the condition. The generator controller provides an indicator and, usually, a common audible signal for conditions it monitors, including a battery or charger failure. This is an obligation on the control system.
- The charger provides alarm contacts. The charger itself presents dry contacts that a monitoring system can read, and the project decides which conditions those contacts represent.
Both arrangements exist, both are common, and they are not interchangeable. If your specification says “charger alarm contacts” but your monitoring scheme expects the controller to annunciate, you will find the gap at commissioning. If it says the reverse, you will find it when the charger arrives without the terminals your panel was built for.
The practical fix is to write the alarm requirement as an outcome rather than a component. State which conditions must be annunciated, where the signal must appear, and whether a common audible alarm is required. Then let the supplier tell you whether the controller or the charger is providing it.
This is an illustrative composite rather than a record of a specific client. A contractor specified a charger with alarm contacts and built the remote monitoring around them. The equipment supplied met the standard and annunciated correctly at the controller, but the charger had no contacts to the terminal block the monitoring panel expected. The system was compliant and the monitoring was not connected. Correcting it meant a wiring change and a second site visit, and the root cause was a clause that named a component instead of a function.
What a Compliant Specification Must Say
Pulling the sections above together, a charger specification that will survive review and commissioning covers these points.
The table mixes two kinds of line: what the standard requires, and what good practice adds on top. Both belong in a specification, but keep the distinction clear in your own mind, because a supplier will answer a clarification differently depending on which kind of line is in dispute.
| Item | What to state |
|---|---|
| Classification | The Level, Type and Class of the system, since the charger requirement inherits from them |
| Edition | Which edition of NFPA 110 the project is governed by, and any local amendment |
| Performance standard | EGSA 100C for the charger; EGSA 100B for the cranking battery |
| Automatic operation | That the charger operates without manual intervention |
| Supply | That the charger’s AC supply is dedicated and monitored, not a circuit that can be isolated unnoticed |
| Recharge window | The window in hours, and the battery capacity it applies to |
| DC load | The standing DC load the charger must carry in addition to recharging |
| Metering | DC ammeter and voltmeter fitted, with the accuracy tolerance stated |
| Marking | The battery capacity range, nominal output, and battery-type data marked on the unit |
| Annunciation | The outcomes required, and where the signal must appear |
| Battery chemistry | The chemistry the charger’s set-points must suit, and whether field adjustment is permitted |
Two of those rows do more work than they look. The marking row matters years later, when the original battery is replaced and the technician needs to know what the charger is set for. Without it, the person replacing the battery has only the charger’s behaviour to go on.
The chemistry row prevents a charger configured for one battery type from receiving another. A flooded battery and a sealed battery have different charging requirements, so a charger set up for one will damage the other even when every other line of the specification is met. The marking and the chemistry line are the two that outlive the project team that wrote them.
How to Verify the Requirement for Your Edition
Because the detail in §5.6 is edition-specific, the last step before a tender goes out is verification. There are four places to look, in order.
- The edition of the standard the project is governed by. Confirm which edition applies, and read the §5.6 starting-equipment provisions in that edition rather than in a summary.
- The annex and the definitions. The classification terms and the recharge requirement are cross-referenced, and the annex often explains the intent behind a clause that reads tersely in the body.
- Local amendments and the authority having jurisdiction. Many projects carry amendments, and the AHJ’s interpretation is what an inspection will follow.
- The project’s own basis-of-design document. If the basis of design states a window or a tolerance, that’s what the supplier will be held to, whatever the standard says.
A specification that has been through those four steps can be defended in a tender clarification. One written from a remembered figure cannot.
Verifying the Charger at Commissioning
The specification decides what is installed. Commissioning decides whether what was installed does what the clause said. Five checks cover the charger, and the last one is the one that takes planning.
- Float stage. With the battery charged, the charger should settle at its float voltage and the current should fall away. If the current holds, the charger isn’t regulating and the battery is being overcharged.
- Equalize or boost stage, if fitted. Confirm it operates and that it is disabled or restricted for any sealed battery on the system.
- Metering. Compare the charger’s own ammeter and voltmeter against an external instrument. Metering that reads plausibly but inaccurately is worse than none, because it is trusted.
- Annunciation, end to end. Trigger each condition the specification names and confirm the signal appears where the specification says it must, not merely that an indicator lights on the unit.
- Recharge. This is the slow one. Confirming that the charger can restore a discharged battery within the window means discharging one, or accepting the manufacturer’s test evidence. Plan it into the commissioning schedule rather than discovering it on the last day.
The annunciation check is the one most often skipped, and it’s the cheapest to run. It’s also the check that would have caught the charger-versus-controller mismatch described above.
Where the charger interacts with the battery’s condition rather than its specification, our guide to a generator battery that keeps going flat covers the diagnostic side, and the generator battery charger guide covers the charger types and set-points themselves.
Frequently Asked Questions
What section of NFPA 110 covers battery chargers?
The battery charging requirements sit in Chapter 5, in the starting-equipment provisions at §5.6. Chapter 5 covers the energy source, the batteries, the charger and the accessories, and §5.6 is the group to read for starting and charging. Cite the section and the edition together, because the text can change between editions, and confirm the exact subsection for your edition.
Does NFPA 110 require a battery charger?
Yes. A system covered by the standard is expected to maintain its starting battery automatically, which in practice means a charger. The engine alternator isn’t a substitute on a standby set, because it only charges while the engine is running.
What is the NFPA 110 recharge time for a battery charger?
The figures commonly applied in project specifications are 24 hours for Level 1 and 36 hours for Level 2. Confirm them against the edition in force before writing them into a tender. The figure you use becomes the minimum charger current once you divide the battery capacity by it and add the standing DC load.
Does the charger or the controller provide the alarms?
Both arrangements exist and they are different requirements. Decide which your project needs, then specify the outcome rather than the component. A clause that names a component can be met while leaving your monitoring scheme unconnected.
Which standard should a generator battery charger be specified against?
EGSA 100C, the performance standard for battery chargers for engine starting batteries and control batteries, with EGSA 100B for the cranking battery. Naming them gives a supplier something to certify against, which a current rating alone does not.
How do I know the requirement I have is current?
Read the §5.6 starting-equipment provisions in the edition your project is governed by, check the annex and any local amendment, and confirm the interpretation with the authority having jurisdiction before the tender closes.
Conclusion
NFPA 110 battery charger requirements are compact, and the difficulty isn’t in reading them. It’s in carrying them into a specification without the details drifting.
Four things matter. The requirement lives in Chapter 5, at §5.6. The system Level decides how strict the recharge obligation is. The window is a sizing input, and the size follows from it. And the alarm requirement should be written as an outcome, because the charger and the controller are not interchangeable.
This is an illustrative composite rather than a record of a specific client. A facilities engineer took over a site mid-project, found a charger specification with no edition cited, and asked the supplier which edition the equipment had been certified against. The supplier answered accurately. The project team then discovered it had been designing to a different edition, and the recharge window in the tender was one of the items that moved. The clause was corrected before the order was placed, at the cost of a phone call rather than a commissioning delay.
Write the classification and the edition first, derive the window from them, then specify the charger against EGSA 100C and state the monitoring outcomes you need. If the result is checked against the edition in force before the tender goes out, the clause will hold.
Contact our engineering team with your system’s Level, battery capacity and standing DC load, and we will tell you what charger the requirement implies before you write it into a specification.
