Yueqing Yijin Electronics Co., Ltd.
How to Select a Single Throw Knife Switch for 3P/4P Isolation
A single throw knife switch is an ON/OFF isolator: each pole has one closed path, and the open position is not a second throw. US search results mostly show 1P classroom kits. A 3P or 4P open knife switch can still be single throw, which is the live Yijin form.
This selection walk counts throw versus poles, rejects changeover hardware when isolation is the job, separates lab SPST kits from power 3P/4P frames, then reads gravity mounting, AC-20B duty, and the HD11F-250 card.
Throw Count Versus Pole Count in Knife Switch Buying
Throw is the number of ON paths each pole can complete. MiniScience’s classroom write-up is blunt: off is not a throw, so a single-throw device is simply ON or OFF.
SparkFun’s pole-and-throw lesson matches that split. Poles are how many separate circuits share the handle. A throw-count is how many positions each of those circuits can land on.
That is why SPST is only the 1P special case. One blade, two terminals, one closed path. Add blades on the same handle and you have a multi-pole single-throw device, not a new throw class.
From the field: Electricians counting exam symbols look at one pole at a time. If that pole can complete only one path, the switch is single throw, even when three or four blades move together. Mike Holt thread on DPDT versus throw counting
A plant that needs L1, L2, and L3 opened together is still shopping a single-throw knife switch isolator. The handle gangs the poles; it does not add a second ON slot.
Single-Throw Isolation Versus Double-Throw Changeover
Double-throw hardware puts the hinge between two jaws so each pole can land on either of two ON paths. Wikipedia’s knife-switch article uses that slot picture: one slot for single throw, two slots for changeover.
Navy electrician courseware draws the same hardware difference. A DPST knife has two blades and one clip set per blade. A double-throw knife has two clip sets so the blades can shift from one circuit to another.
Buy double throw when the job is source A or source B, or load A or load B. Buy single throw when the job is isolate this feeder and leave it open.
AudioKarma’s stereo-switch thread makes the pole mistake in the other direction. Users asked for a DPDT knife and were told they needed 4PDT if four paths each needed two throws. Extra poles never turn HD11F into a changeover switch.
Yijin already published a double pole double throw knife switch walk for true changeover language. This page stays on single-throw isolation.
Lab SPST Kits Versus Open 3P/4P Power Knives
Classroom catalogs sell the search term as a plastic-base demo switch. LabPro’s SPST knife is specified for experiments less than 3.6 V, and Geyer and Flinn sell the same throw-by-pole grid.
Those kits teach the words. They do not carry a plant feeder.
The cataloged SKU behind this query is HD11F. The live series is an open knife switch for infrequent manual isolation, not a binding-post demo. The table lists HD11F-250/4 or HD11F-250/3, and the pole row is 3P and 4P only.
Do not order HD11F as 1P SPST or 2P DPST. Those frames are not on the table.
A buyer who landed here from what is a knife switch already has the blade-and-jaw picture. The remaining decision is whether the search term matches that classroom kit or a 3P/4P isolator.
Keep the classroom kit on the bench for teaching the words, and keep HD11F for isolation current.
Use the selection map before an RFQ leaves the desk.
| What you counted | What you actually bought | Fits HD11F-250? |
|---|---|---|
| One throw, one pole | Classroom SPST kit | No. Table has no 1P. |
| One throw, two poles | DPST lab or enclosed 2P disconnect | No. Table is 3P/4P only. |
| One throw, three poles | 3P single-throw isolator | Yes, order HD11F-250/3. |
| One throw, four poles | 4P single-throw isolator | Yes, order HD11F-250/4. |
| Two throws per pole | Double-throw changeover | No. HD11F is not DPDT. |
Gravity and Mounting Rules for Single-Throw Blades
Single-throw knives must sit so gravity cannot slam the blades closed. California Title 8 §2480.5 states that rule in one sentence, and UpCodes restates the same single-throw mounting language.
Inverted mounting is a separate case. The code text wants a locking device that keeps the blades open when the switch is set that way.
The HD11F body stays an open, protective-opening form, so the hinge direction still matters even though the series is not a listed US safety switch. Put the hinge where a dropped handle falls away from the jaws, not into them.
OSHA lockout then treats that open isolator as an energy isolating device held in OFF. HD11F supplies the isolation contacts. It does not publish a padlockable enclosure listing.
AC-20B Compatibility for HD11F Open Knives
Use HD11F when isolation happens after another device already stopped current. The product copy says infrequent manual connection, disconnection, and isolation on AC 50 Hz, rated voltage up to 400 V, and operation under no-load.
Utilization category AC-20B is the table’s name for that no-load duty. It is not motor-breaking AC-23 and not a substitute for a circuit breaker.
IEC 60947-3 covers switches, disconnectors, switch-disconnectors, and fuse-combination units up to 1000 V AC. The same standard’s Note 2 calls a knife-switch disconnector a design name beside rotary and cam forms.
HD11F is specified to GB/T14048.3 and IEC 60947-3 on the product page. That is first-party standard language, not a third-party certificate file, and it does not make the SKU a rotary cam.
Wikipedia’s disconnector article is the plain version: open the isolator after current is already interrupted. A feeder breaker or contactor does the stopping; the open knife holds the visible gap.
Skip HD11F when the spec sheet wants on-load make/break, a UL-listed safety switch, or a cam rotary handle. Those jobs are outside this SKU.
HD11F-250 3P and 4P Parameter Card
HD11F-250 is the live open-knife frame with two pole orders. /3 is three poles. /4 is four poles.
The heating current on that frame is 250 A.
The table lists Ue 400 V, Ui 1000 V, Ith 250 A, Uimp 8 kV, and 50 Hz. Rated working current steps are 160 A, 180 A, 200 A, 225 A, and 250 A.
Icw is 3 kA. Mechanical life is 10000 operations. Ambient air is −25 °C to +70 °C, with altitude not above 2000 m.
Ignore the polluted Product Introduction that talks about WIFI reclosing. That leftover copy is wrong for this SKU.
| Item | HD11F-250 published value |
|---|---|
| Model | HD11F-250/4 or HD11F-250/3 |
| Poles | 3P, 4P |
| Ue | 400 V |
| Ui | 1000 V |
| Ith | 250 A |
| Rated working current | 160 A, 180 A, 200 A, 225 A, 250 A |
| Frequency | 50 Hz |
| Uimp | 8 kV |
| Utilization category | AC-20B |
| Icw | 3 kA |
| Mechanical life | 10000 |
| Standards named on the page | GB/T14048.3, IEC 60947-3 |
Order the current step on the nameplate, not a nearby frame from another family. A 3ph+N machine that must open the neutral with the phases takes /4. A three-phase feeder that leaves N solid takes /3.
Product recommendation: HD11F-250 for Single-Throw Open Knife Isolation
Choose the HD11F-250 open knife isolator when the search term was a single throw knife switch and the real job is 3P or 4P no-load isolation.
Specify HD11F-250/3 or HD11F-250/4, the Ue, and the working current from the 160–250 A list. The isolating switch hub is the catalog parent for that SKU.
Do not use this recommendation for a classroom SPST kit, a double-throw transfer, a rotary cam, or a UL/NEC listed enclosed safety switch. HD11F does not publish those listings.
One natural next step is the product page. Contact only if the pole count or current step still needs a human check.
FAQ
What is a single throw knife switch?
It is an ON/OFF knife whose each pole completes one path. The blade sits in one jaw or sits open.
Is a single throw knife switch the same as SPST?
SPST is the one-pole case. A 3P or 4P knife can still be single throw because throw is counted per pole.
Can a 3-pole or 4-pole knife still be single throw?
Yes. Extra blades add poles on one handle. HD11F-250 is sold as 3P or 4P, both single throw.
When do I need double throw instead of single throw?
Use double throw to choose between two ON paths. Isolation of one feeder is still single throw.
Are classroom SPST knives the same as HD11F?
No. Education kits such as LabPro are specified under 3.6 V. HD11F is a 3P/4P power isolator on AC-20B duty.
Why operate HD11F under no-load?
The series copy requires no-load operation, and the table lists utilization category AC-20B. Open it after another device already stopped current.
Does HD11F come in 1P or 2P?
No. The live table lists 3P and 4P only.
Is HD11F UL listed or NEC listed?
No UL listing or NEC disconnect listing is published for this SKU. Title 8 gravity language is market context, not a Yijin listing.
How should a single-throw knife be mounted so gravity cannot close it?
Place it so gravity will not tend to close the blades. Inverted use needs a hold-open lock in the US single-throw code text.
Can HD11F replace a circuit breaker?
No. An isolator holds an open path. Overcurrent interruption stays with a circuit breaker.
What ambient and altitude window does HD11F publish?
Ambient air −25 °C to +70 °C, altitude not above 2000 m.
References
- Wikipedia: Knife switch — single-throw one slot, double-throw two slots, multi-pole ganged knives.
- SparkFun: Poles and throws — poles as circuits, throws as positions, SPST ON/OFF.
- IEC 60947-3 webstore — LV switches, disconnectors, switch-disconnectors up to 1000 V AC.
- IEC 60947-3 preview PDF — Note 2 lists knife-switch disconnectors among the design names for this device class.
- California Title 8 §2480.5 Single-Throw Knife Switches — gravity must not close single-throw blades.
- OSHA 1910.147 — lockout holds energy isolating devices in OFF.
- Wikipedia: Disconnector — off-load isolator, not a circuit breaker.
- Mike Holt: Double pole double throw switch — count one path per pole to name the throw.
