BS88 Fuse Sizes and Body Types
What BS88 fuse size really means
When people search for BS88 fuse sizes, they usually need to identify an old fuse link, confirm what holder it fits, or find a safe replacement. The visible body size matters, but it cannot be separated from the circuit. A BS88 fuse link has a mechanical identity and an electrical identity at the same time.
The mechanical identity includes body length, body diameter or width, tag form, fixing centres, blade shape, bolted connection and the matching fuse holder or carrier. The electrical identity includes current rating, voltage rating, AC or DC duty, breaking capacity and utilisation class such as gG, gM, aM, aR or gR.
This is why a good BS88 size guide should do more than list dimensions. A list helps you recognise the part. A replacement decision needs the holder, the protected circuit and the data sheet. The practical rule is simple: size proves possible fit, not full equivalence.
A BS88 size check has five layers
| Layer | What to check | Why it matters |
|---|---|---|
| Size reference | A1, A2, A3, A4, E1, F1, F2 or another family mark. | Points to a likely body and holder family. |
| Fixing centres | Distance between fixing holes or contact points on bolted tags. | Prevents a mechanically wrong fuse being forced into the carrier. |
| Tag or blade form | Offset, central, blade, bolted or compact format. | Defines how the fuse makes contact with the holder. |
| Electrical rating | Current, voltage, AC or DC duty and breaking capacity. | Confirms the fuse is safe for the circuit, not just the holder. |
| Application class | gG, gM, aM, aR, gR or manufacturer-specific duty. | Prevents mixing cable, motor and semiconductor protection duties. |
BS88 size families at a glance
| Reference | Common role | What still needs checking |
|---|---|---|
| E1 / F1 / F2 | Compact BS88 style links and smaller holder systems. | Blade or tag geometry, voltage, current, class and exact series. |
| A1 | Smaller offset-tag family. | 44.5 mm reference, body size, holder model and rating. |
| A2 | Mid-size offset or bolted family. | 73 mm reference plus body and current range. |
| A3 | Another 73 mm family with different fit logic from A2. | Never assume interchangeability with A2. |
| A4 | Larger offset-tag family. | 94 mm reference, heat history, torque and holder condition. |
BS88 A1, A2, A3 and A4 fixing centres
For many British style BS88 compatibility references, the common bolted or offset tag fixing centres are 44.5 mm for A1, 73 mm for A2, 73 mm for A3 and 94 mm for A4. These values are useful because they can be checked with a ruler or caliper after the fuse is safely removed.
The trap is that a fixing-centre distance describes only one mechanical dimension. It does not describe the body diameter, body length, tag thickness, current range, heat dissipation, voltage duty or holder family. If the old label is damaged, the fuse carrier and panel documentation become more important.
Use fixing centres to avoid obvious mechanical mistakes. Then use the full marking and manufacturer data to confirm the actual replacement. A correct BS88 replacement is a system match, not a single number match.
| BS88 size reference | Common fixing-centre value | Typical practical note | Do not ignore |
|---|---|---|---|
| A1 | 44.5 mm | Common small offset tag reference. | Holder shape, current rating and voltage duty. |
| A2 | 73 mm | Mid-size reference often used in industrial gear. | May share centre distance with A3. |
| A3 | 73 mm | Different family from A2 despite the same common centre value. | Body size, current range and carrier compatibility. |
| A4 | 94 mm | Larger offset tag reference. | Thermal condition, torque and contact pressure. |
Why A2 and A3 are a common trap
The most dangerous simplified BS88 size advice is to measure 73 mm and assume the replacement is solved. In many references, both A2 and A3 may appear with 73 mm fixing centres. That shared dimension is useful for recognition, but it does not prove that the two links can be swapped.
A2 and A3 can differ by body size, current range, tag proportions, holder design, contact area and heat behaviour. A holder that accepts one family may not properly support another. Even if a fuse can be physically installed, poor contact pressure or reduced surface contact can create heating at normal load.
For this reason, A2 versus A3 should be treated as a specific identification step. Record the old fuse marking, photograph the holder, measure the body, check the series code and compare the data sheet. Do not let the shared 73 mm figure become the whole decision.
| Question | Why it matters | Safe action |
|---|---|---|
| Does the old fuse marking clearly say A2 or A3? | The same fixing distance can appear in both families. | Copy the full code and compare the exact series. |
| Is the body length and diameter the same? | The holder may position the contact surfaces differently. | Measure the body, not only the tags. |
| Is the current range the same? | Thermal behaviour changes with body and contact area. | Check the data sheet, carrier and panel schedule. |
| Are there heat marks in the holder? | A near-fit can overheat even when it carries load current. | Inspect or replace damaged carriers before fitting a new fuse. |
Compact BS88 sizes: E1, F1 and F2
| Reference | Practical clue | Replacement risk |
|---|---|---|
| E1 | Small compact offset or blade style family in many charts. | Easy to confuse with similar looking compact links from another series. |
| F1 | Compact BS88 style link used where space and holder design are specific. | The blade or tag form may look close but not seat correctly. |
| F2 | Related compact reference with its own body and holder expectations. | Do not choose from a photo alone. |
| B / C / D | Larger bolted formats appear in some cross-reference material. | Current range, torque, contact surface and fault duty become critical. |
E1, F1 and F2 references are often seen when people are trying to identify compact BS88 fuse links. They can be more confusing than the larger A-family references because the body may be small, the markings may be partly hidden, and the holder may be an older proprietary arrangement.
The safest process is the same: remove the fuse only under safe isolation, record the full marking, photograph the holder and carrier, measure the body and tags, then compare the candidate replacement against a data sheet. Compact size does not make the replacement less important. In fact, compact holders can be less forgiving of poor contact or wrong blade geometry.
If the old part number is unreadable, the holder label and original panel documentation may be the best evidence. A cross-reference table can help narrow the candidate family, but it should not be treated as a final approval.
How to measure a BS88 fuse size
Before measuring, the circuit must be isolated and made safe by a competent person. Once the fuse is removed safely, start with photographs. Take one photo of the complete fuse, one close photo of the marking, one of each tag or blade end, and one of the holder or carrier.
Measure fixing centres from the centre of one fixing hole or contact point to the centre of the other. Measure body length separately from overall length. Record body diameter or width, tag thickness, tag offset and any visible series code. If the fuse uses a carrier, record the carrier model and any heat marks around contacts or screws.
The best record is not a single dimension. It is a small replacement file: old marking, photos, measured fixing centres, body dimensions, holder model, circuit voltage, current, class and fault-duty requirement.
| Measure or record | How to use it | Common mistake |
|---|---|---|
| Full printed marking | Confirms current, voltage, class, standard and possible series. | Relying on body colour or approximate shape. |
| Fixing centres | Identifies likely A-family or bolted tag geometry. | Assuming 73 mm means both A2 and A3 are safe. |
| Body length and diameter | Confirms the fuse sits correctly in the carrier. | Measuring only the overall tag-to-tag length. |
| Tag form and offset | Confirms contact position and mechanical fit. | Forcing a near-fit into an older holder. |
| Holder or carrier model | Connects the fuse to the equipment design. | Ignoring holder damage and replacing only the fuse. |
Body size is not current rating
| If two BS88 fuses have the same amp rating | They may still differ by | Why that matters |
|---|---|---|
| Same 63 A marking | Different voltage rating. | The wrong fuse may not safely interrupt the circuit voltage. |
| Same 100 A marking | Different body or tag form. | The fuse may not fit the holder or may have poor contact. |
| Same 160 A marking | Different class such as gG, aM or aR. | The protection behaviour can be wrong for cables, motors or semiconductors. |
| Same 200 A marking | Different breaking capacity. | The fuse may be unsafe for the available short-circuit current. |
Holder fit and contact condition
A BS88 fuse size guide is incomplete unless it discusses the holder. The fuse and holder work as a pair. The holder gives mechanical support, contact pressure, heat transfer and safe spacing. If the contact surface is weak, dirty, loose or heat damaged, a correct fuse link can still run hot.
Look for discoloured clips, melted plastic, cracked ceramic, loose screws, pitted contact surfaces, missing shrouds and carriers that no longer grip the link properly. Repeated fuse operation is also a warning sign. The cause may be the circuit, the holder, the environment or a wrong previous replacement.
For larger A4 and higher-current BS88 applications, holder condition becomes especially important. Current, enclosure temperature and contact pressure all influence heating. A replacement decision should include the physical condition of the fusegear, not only the catalogue line.
| Holder condition | What it may mean | What to do |
|---|---|---|
| Darkened contacts | Possible overheating or poor contact pressure. | Investigate the holder before fitting a new link. |
| Loose screws or carriers | Mechanical connection may be unreliable. | Check torque and manufacturer instructions. |
| Cracked shrouds | Reduced safety around live parts. | Replace damaged components before service. |
| Wrong previous fuse | The installed link may not reflect the original design. | Use drawings, equipment label and fusegear data. |
BS88 cross-reference without the usual mistakes
Cross-reference tables are useful when an old Lawson, MEM, Bussmann, Eaton, Mersen or other BS88 part number is hard to find. They can point to a likely modern equivalent or a similar manufacturer series. The mistake is treating that line as complete proof.
A proper cross-reference still needs the same checks: standard reference, current, voltage, AC or DC duty, breaking capacity, utilisation class, body type, tag geometry, fixing centres, holder model and application. For semiconductor or drive circuits, I²t and high-speed behaviour also matter.
The safest wording is candidate equivalent until the data sheet and installation have been checked. This is more precise than saying two fuses are the same because they share a size code.
| Step | Question | Pass condition |
|---|---|---|
| 1. Identify | What is the old fuse marking and size reference? | Full code or strong evidence from holder and panel data. |
| 2. Measure | Do body, tags and fixing centres match? | No forced fit, no missing contact area, no carrier conflict. |
| 3. Compare | Do electrical ratings match the circuit? | Current, voltage, AC or DC duty and breaking capacity confirmed. |
| 4. Match class | Is the utilisation class right? | gG, gM, aM, aR or gR chosen for the application. |
| 5. Inspect | Is the holder safe? | No heat damage, weak contact, broken carrier or wrong base. |
| 6. Document | Can the choice be explained later? | Record photos, measurements, data sheet and circuit duty. |
BS88 fuse size selection table
| Situation | Most important size check | Most important electrical check | Likely supporting page |
|---|---|---|---|
| Old fuse is intact and readable. | Copy size reference, body and fixing centres. | Confirm current, voltage, class and breaking capacity. | BS88 fuses |
| Old label is burned or missing. | Use holder model, carrier and panel documentation. | Do not assume the installed fuse was correct. | Fuse cross-reference guide |
| A2 or A3 appears possible. | Do not rely on 73 mm alone. | Compare body, current range and holder fit. | Fuse holder guide |
| Fuse is near main supply or transformer. | Confirm holder and fuse family. | Check prospective fault current and breaking capacity. | Fuse breaking capacity |
| DC, battery or PV circuit. | Confirm physical fit and insulation distance. | Use explicit DC voltage and DC breaking data. | DC fuses vs AC fuses |
Common BS88 size mistakes
The same amp rating can appear in different bodies, classes, voltages and breaking capacities.
A2 and A3 may share a common fixing-centre value but still need separate identification.
Heat marks, weak clips and loose contacts can defeat a correct fuse selection.
A fuse that fits the holder may still be wrong for DC interruption.
Photos can hide tag thickness, offset, body length and holder differences.
A recorded decision is easier to review when the panel is serviced again.
Common questions about BS88 fuse sizes
What are BS88 fuse sizes?
BS88 fuse sizes are practical body and tag references used to identify whether a fuse link will fit a specific holder or carrier. The size reference must be checked with the electrical rating, voltage, breaking capacity and application class.
Are A1, A2, A3 and A4 BS88 fuses interchangeable?
No. A1, A2, A3 and A4 are not automatically interchangeable. They may differ by body length, current range, tag geometry, holder design and fixing centres.
What are the common fixing centres for BS88 bolted fuses?
Common UK BS88 style references often use 44.5 mm for A1, 73 mm for A2 and A3, and 94 mm for A4. The exact manufacturer data and holder must still be checked.
Why are A2 and A3 BS88 fuses a common replacement trap?
A2 and A3 may both be seen with 73 mm fixing centres, but they can differ in body size, current range, thermal behaviour and holder compatibility. Matching the distance alone is not enough.
Can I choose a BS88 replacement by amp rating only?
No. The replacement must match current rating, voltage rating, breaking capacity, utilisation class, body size, tag form, fixing centres and holder condition.
What are E1, F1 and F2 BS88 sizes?
E1, F1 and F2 are compact BS88 style references commonly associated with smaller offset or blade type fuse links. The exact body and holder must be confirmed from the marked part and manufacturer data.
What should be measured before replacing a BS88 fuse?
Record the full fuse marking, body length, diameter or width, tag form, fixing centres, holder model, current rating, voltage rating, class and any heat damage around the carrier.
Do BS88 fuse sizes prove short circuit capacity?
No. Size helps identify fit and family. Short circuit suitability is checked through breaking capacity, voltage rating, AC or DC duty and the prospective fault current at the installation point.
Bottom line
BS88 fuse size is a starting point, not the whole replacement decision. A1, A2, A3, A4, E1, F1 and F2 references help identify the physical family, but the safe choice also depends on holder fit, voltage, breaking capacity, utilisation class and the protected circuit.
The strongest habit is to document the old fuse before choosing the new one. Record the marking, size, fixing centres, holder model and circuit duty. Then use cross-reference data as a candidate route, not as a blind substitution.