What Types of Battery Are Used in Emergency Lighting?

Emergency lighting relies on various battery types, with the main ones being:

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1. Lead Acid: These were commonly used in self-contained emergency lighting fixtures, such as twinspots, and are still widely used in central battery systems. Outside these applications, lead acid batteries are now rarely used in emergency lighting.

- Example: A twinspot emergency light fitting. Until recently, most of these used sealed lead acid batteries, but other chemistries are now being used.

2. Nickel Cadmium (NiCd): Despite cadmium being highly toxic and banned by the EU’s RoHS Directive, an exemption is in place for emergency lighting batteries due to limited alternatives. NiCd batteries are widely used in standalone emergency lighting fixtures and emergency conversion kits.

- Example: A standalone emergency exit sign with nickel cadmium (NiCd) batteries inside the fitting.

- Example: NiCd batteries in conversion kits used to turn standard light fittings into emergency lights, typically consisting of 2, 3, or 4 cells.

3. Nickel Metal Hydride (NiMH): These batteries are increasingly used instead of NiCd in emergency conversion kits due to slight advantages in some applications.

- Example: A NiMH battery consisting of 5 cells. NiMH cells are slimmer than NiCd cells.

4. Lithium: There are many types of lithium battery and they are becoming more widely used for emergency lighting. They have many advantages over lead acid, NiCd and NiMH so their use is increasing rapidly.

Are Lithium Iron Phosphate (LFP) Batteries Suitable for Emergency Lighting?

Lithium iron phosphate (LiFePO4, or LFP) batteries are highly suitable for emergency lighting, offering several advantages over NiCd and NiMH batteries:

- Energy Efficiency: LFP batteries are more efficient than NiCd batteries. They have a self-discharge rate of only 3-5% per month compared to NiCd's 15% in the first 24 hours and 10-20% per month thereafter. This means the charger in an LFP circuit works less frequently, conserving energy.

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- Charge Efficiency: LFP batteries have a high charge efficiency of about 95%. NiCd batteries start with high efficiency, but it drops to around 85% after reaching 70% capacity. This inefficiency in NiCd batteries results in more energy loss during continuous trickle charging.

- Long Life: LFP batteries experience little memory effect and maintain performance until the end of life, typically 8-10 years. In contrast, NiCd and NiMH batteries' performance declines with each charge/discharge cycle, often requiring replacement after 3-4 years.

- Extreme Temperature Performance: LFP batteries operate well up to 60ºC and down to -20ºC, whereas NiCd and NiMH batteries can only tolerate up to 55ºC and 50ºC and perform poorly below 0ºC.

- Environmental Impact: Cadmium, used in NiCd batteries, is highly toxic and persistent in the environment, requiring careful recycling. LFP batteries, while also needing recycling, use less harmful materials.

- Future Use: With superior alternatives like LFP available, it is expected that the RoHS directive will eventually eliminate the exemption for cadmium in emergency lighting batteries.

LiFePO4 or LiFePO₄- What's the Difference?

LiFePO₄ is the correct chemical formula for lithium iron phosphate, indicating 4 oxygen atoms (O) bound to one phosphorus atom (P). However, LiFePO4 is commonly used in text due to the difficulty of typing the subscript.

Costs of Using Lithium Iron Phosphate (LFP) Batteries in Emergency Lighting

Lithium iron phosphate is cost-effective for emergency lighting, considering acquisition, running, and maintenance costs:

- Acquisition Costs: Over a period of 4+ years, LFP batteries are cheaper than NiCd batteries. Although LFP batteries have a higher initial cost based on capacity (Ah), their longer lifespan and stable performance make them more economical over time.

- Running Costs: LFP batteries have lower running costs due to their low self-discharge rate, reducing the need for constant charging. Tests show that using LFP batteries in emergency light fittings can save over 40% in power consumption compared to NiCd batteries, translating to an annual saving of £2.25 per fitting at an electricity price of £0.145 per kWh.

- Maintenance Costs: LFP batteries have lower maintenance costs because their lifespan is typically 8-10 years, compared to just 4 years for NiCd batteries. This results in maintenance costs being 50% or less than those of NiCd batteries.

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Re: Emergency Lighting

Originally posted by websparky:
and there is an emergency generator tied into the normal power system,

Dave I am not sure what you mean by that.

Is it installed as Article 700 requires (entirely separate) or is it installed as per Article 702 (mixed)?

IMO if it is 'mixed' than you do not have an emergency system so you must have battery units.

If it is an article 700 system no battery units are required but are a nice supplement.

My code reference would be 700.12(A) through (E)

700.12 requires the source of power to be at least one of the listed supplies Storage Battery, Generator Set, Uninterruptible Power Supplies, Separate Service or Unit Equipment (EBUs).

part of 700.12

The supply system for emergency purposes, in addition to the normal services to the building and meeting the general requirements of this section, shall be one or more of the types of systems described in 700.12(A) through (D). Unit equipment in accordance with 700.12(E) shall satisfy the applicable requirements of this article.

Re: Emergency Lighting

I have never seen battery equipment required when the building has an emergency system in place.

I feel that is the reason there is 700.12(B)(5).

700.12(B)(5) Auxiliary Power Supply. Generator sets that require more than 10 seconds to develop power shall be permitted if an auxiliary power supply energizes the emergency system until the generator can pick up the load.

I believe as far as the NEC is concerned we can have the building 'black' for 10 seconds.

But...we have long since established the rules in my area (or how they are applied) are not always in sync with your area.

I do see the issue you bring up with the building code.

shall be illuminated at all times

What happens if we have to work on the circuit?

Would we have to evacuate the space first? Re: Emergency Lighting

Originally posted by websparky:
Now let's take a different case. Say a feeder trips to a panel that supplies power to an entire floor of the building. This event will not call on the generator to start and run to supply emergency lighting. Now what?

Now what?

The area that emergency feeder supplies is in the dark.

The problem that you describe I believe is the driving force in keeping the emergency system as limited as possible and not mixing it with the normal systems.

All I can go by is what I have seen and to be honest I have seen and worked on many large buildings that use only generator back up.

I am confident in this area (New England) that battery units are not required in buildings with another type of emergency system in place.

Give me some credit Dave I understand the shortcomings of generator supplied emergency systems. I work on them frequently in January I will be installing a 500 KVA emergency / standby generator in an existing facility.

The most common problem is the generator not starting when needed. This was very much brought to the forefront when the last big black out happened in the North East. Many places where left in the dark.

But battery units are also junk if they are not properly maintained.

I personally like to see EBUs backed up by generator but I feel that is a design choice and not a code requirement.

[ December 24, , 07:08 PM: Message edited by: iwire ] Re: Emergency Lighting

Here is what I have found:

NFPA 101 Life Safety Code
7.9.2.2*
The emergency lighting system shall be arranged to provide the required illumination automatically in the event of any of the following:
(1) Interruption of normal lighting such as any failure of a public utility or other outside electrical power supply
(2) Opening of a circuit breaker or fuse
(3) Manual act(s), including accidental opening of a switch controlling normal lighting facilities

7.9.2.5
The emergency lighting system shall be either continuously in operation or shall be capable of repeated automatic operation without manual intervention.

The * above referes you to the Appendix for further explanation.

A.7.9.2.2
Where approved by the authority having jurisdiction, this requirement is permitted to be met by means such as the following.
(a) Two separate electric lighting systems with independent wiring, each adequate alone to provide the specified lighting. One such system is permitted to be supplied from an outside source such as a public utility service and the other from an electric generator on the premises driven by an independent source of power. Both sources of illumination should be in regular simultaneous operation whenever the building is occupied during periods of darkness.
(b) An electric circuit or circuits used only for means of egress illumination, with two independent electric sources arranged so that, on the failure of one, the other will automatically and immediately operate. One such source is permitted to be a connection from a public utility or similar outside power source and the other an approved storage battery with suitable provision to keep it automatically charged. Such a battery should be provided with automatic controls that, after operation of the battery due to failure of the primary power source or to turn-off the primary electric source for the lights, the battery will be shut off after its specified period of operation and will be automatically recharged and ready for further service when the primary current source is turned on again.
(c) Electric battery-operated emergency lighting systems complying with the provisions of 7.9.2.2 and operating on a separate circuit and at a voltage different from that of the primary light can be used where permitted. (See NFPA 70, National Electrical Code ?.)
These requirements are not intended to prohibit the connection of a feeder serving exit lighting and similar emergency functions ahead of the service disconnecting means, but such provision does not constitute an acceptable alternate source of power. Such a connection furnishes only supplementary protection for emergency electrical functions, particularly where intended to allow the fire department to open the main disconnect without hampering exit activities. Provision should be made to alert the fire department that certain power and lighting is fed by an emergency generator and will continue operation after the service disconnect is opened.
Where emergency lighting is provided by automatic transfer between normal power service and an emergency generator, it is the intent to prohibit the installation, for any reason, of a single switch that can interrupt both energy sources.

Re: Emergency Lighting

Dave

A.7.9.2.2
Where approved by the authority having jurisdiction, this requirement is permitted to be met by means such as the following.

(a) Two separate electric lighting systems with independent wiring, each adequate alone to provide the specified lighting. One such system is permitted to be supplied from an outside source such as a public utility service and the other from an electric generator on the premises driven by an independent source of power. Both sources of illumination should be in regular simultaneous operation whenever the

I think that backs up my opinion that battery units are not required when a generator supplied lighting system is in place.


What do think it says?

By the way is NFPA 101 adopted in your area?

The NFPA has dozens of codes none of which mean much unless adopted.