i5 Insulation Resistance Testing: HV Safety Maintenance for Electric Truck Fleets

The SAGMOTO i5 electric light and medium duty truck, rated at 120 to 160 kilowatts with a 100 to 140 kilowatt hour battery, is distributed internationally by Shaanxi Fenghan Trading Co., Ltd., whose export licence USCC 91610132MAB0X7XG1M covers the new energy line. Unlike a diesel, the i5 carries a high-voltage traction bus that can exceed 600 volts, and the only thing standing between that bus and the chassis is the insulation of the cables, connectors and components. Insulation resistance testing is the routine that confirms that barrier is intact, and it is the single most important safety check an electric truck fleet runs. This article sets out the megohm-meter procedure, the acceptance values, the test points, the BMS thresholds, the test triggers, the PPE and lockout, the drying procedure and the records an operator should keep. Fleets planning a conversion can review the SAGMOTO new energy electric trucks range before specifying the i5.

Why insulation resistance matters on the i5

The i5 high-voltage system includes the battery pack, the motor inverter, the traction motor, the DC-DC converter and the air-conditioning compressor, all joined by orange-coded HV cabling that must remain isolated from the conductive frame. If that insulation degrades, a fault current can flow through the chassis to a person who touches the truck, and the risk rises sharply after water ingress, after a crash, or as connectors age in humid tropical service. A megohm-meter measures the resistance between the HV conductors and the frame, and a falling trend is the early warning that a cable or connector is about to fail. Treating insulation resistance as a scheduled safety routine, rather than a fault-finding step after an incident, is what keeps an electric fleet safe and insurable, and it is a requirement many overseas insurers now ask for in writing. The i5 uses orange-highlighted HV cabling throughout, and the number of connectors multiplied by the vibration of urban delivery duty is the main source of slow insulation drift, which is exactly why a scheduled test beats a reactive one.

A fleet that measures monthly in the first year builds a baseline that makes later faults obvious, whereas a fleet that never measures has no way to tell a safe reading from a dangerous one.

Megohm-meter test voltage and acceptance values

The i5 HV bus should be tested with a 1000 volt DC insulation tester, the class appropriate to a traction system that operates above 600 volts, because a lower test voltage hides defects that only appear under real operating stress. Apply the test between each HV pole and the frame with the system de-energised and locked out, and read the resistance after the initial charge transient settles, typically within 30 to 60 seconds. A typical acceptance value for the i5 is above 1 megohm on the HV bus to frame, with many operators holding a 500 kilohm to 1 megohm minimum depending on the local standard and the component being measured, and any reading below that threshold removes the vehicle from service. Record the temperature, because resistance falls as the insulation warms and a cold reading taken on a hot day misleads the trend.

Test points across the HV bus

The test must cover every isolated section, not just the battery, because a single chafed motor-phase lead or a damp inverter connector will drag the whole-bus reading down once measured end to end. Measure the positive and negative bus to frame at the battery disconnect, at the inverter, at the motor, and at the compressor and DC-DC converter, and compare each to its own baseline rather than only the system total. A good practice is to open the section isolators and test each segment alone, which localises a fault to one component instead of sending a technician hunting through the whole loom. Tag each test point with a durable label and a number, because the same points must be used every time so the readings are comparable across months and across the fleet. Where the i5 carries a rear-motor variant the test point list changes, so the workshop should keep a model-specific map rather than assuming the points are identical.

Segment testing takes longer than a single end-to-end check but pays back the first time it finds a damp motor connector in ten minutes instead of a day.

BMS isolation monitoring thresholds

The i5 battery management system already watches isolation continuously while the truck is awake, and it will flag a fault and often disable drive if the live isolation drops below its internal threshold, which is typically set well above the workshop acceptance minimum to give advance warning. The fleet should read this BMS isolation value during every periodic diagnostic download and trend it alongside the manual megohm-meter readings, because the BMS sees the system under operating voltage while the meter sees it de-energised. A BMS value that drifts downward between services is the earliest signal of moisture or connector oxidation, and acting on it prevents the roadside isolation fault that strands a delivery. Document the BMS threshold from the service manual so the workshop knows the difference between a harmless transient and a genuine degradation that needs the manual test to locate. Because the BMS threshold is set conservatively, a truck that passes the workshop meter can still log a BMS isolation warning in service, and the workshop should investigate those warnings rather than clearing them, since they are the system reporting the very trend the manual test is meant to catch.

When to test: triggers and intervals

Schedule a full insulation test at least annually as part of the high-voltage PM, and add a test after any event that could let moisture or damage reach the HV system: a fording or flood event, a pressure wash that wets a connector, a crash or recovery, or any opened HV connector during repair. The i5 should also be re-tested after a period in storage, especially in humid or coastal depots where condensation forms inside unsealed connectors, and after any coolant leak near the inverter or motor because the glycol is conductive. Treat the test as cheap insurance compared with a stuck vehicle or an injury claim, and never return a truck to service after water ingress without a passing reading and a dry-out record. A practical rule is to test on the first working day after any heavy rain if the depot has open-sided parking.

Keep the trigger list posted in the bay so drivers and technicians both know which events force a test, because the test is only useful if it is actually performed after the event that makes it necessary.

PPE and lockout procedure

Before any HV work the technician must be trained to the local electric-vehicle standard and equipped with rated gloves, a face shield, insulated tools and a voltage detector that is proved on a known source before and after use. Lockout means opening the manual service disconnect, locking it off, waiting the specified capacitor-bleed time, then proving the bus dead with the detector at every test point before touching anything. Only then is the megohm-meter connected, and the tester itself must be rated for the 1000 volt class. A second person should be within call and a rescue plan in place, because a fallen technician in contact with a live bus cannot help themselves. The lockout sequence is specific to the i5 battery contactor and the manual disconnect location, and a generic EV lockout from another brand will not match the physical layout, so the i5 manual must be followed point by point rather than from memory.

Drying-out procedure after ingress

If a test after water ingress reads low, the first response is to dry the system before assuming a hard fault, because many connectors and cable ends recover once the moisture is removed and the reading climbs back above the threshold. Remove the affected connectors, blow them out with clean dry air, apply a conductive-neutral contact treatment if specified, and let the compartments breathe in a warm dry space for the time the manual recommends, then re-test before reconnection. Do not force a heat gun close to a sealed connector or a cell, because local overheating damages the seal and the battery, and a slow controlled dry beats a fast harsh one. If the reading does not recover after the specified dry-out, replace the connector or loom section rather than returning the truck, because a marginal insulation that passed once will fail again on the next damp morning. After a dry-out and a passing re-test, note the event and the recovery time in the log, because a connector that needed drying once will likely need it again after the next flood, and the trend tells the fleet whether to relocate a seal or re-route a loom.

Documentation and fleet record keeping

Every insulation test should be logged with the VIN, the date, the ambient and component temperature, the test voltage, each measured value, the BMS reading, the technician name and the pass or fail result, because that record is what an insurer or regulator will ask for after any HV incident. Keep the readings in a fleet spreadsheet so a downward trend on one vehicle is visible across the whole i5 fleet, and use it to justify pre-emptive connector service before a failure. Shaanxi Fenghan Trading can provide the i5 test template keyed to the VIN so the columns match the manual thresholds, and a disciplined log is the difference between a fleet that can prove its safety routine and one that simply hopes the insulation holds.