IP66 vs IP51
Head-to-head comparison of two IEC 60529 ingress protection ratings.
IP66 and IP51 are both IEC 60529 ingress protection codes, but they differ in solid-object protection (level 6 vs 5) and liquid protection (level 6 vs 1). IP66 is rated for dust-tight and powerful water jets (12.5 mm nozzle), while IP51 provides dust-protected and vertically dripping water.
IP66 is dust-tight and resists powerful water jets (12.5 mm nozzle, 100 kPa). A robust outdoor rating for equipment exposed to heavy rain, storms, or directed high-pressure hosing (but not high-pressure washdown).
With IP51, an enclosure receives dust-protected (limited ingress, no harmful deposit) and protection against vertically falling drops of water. Dripping water shall have no harmful effects.. It is an IEC 60529 ingress protection code combining first-digit (solid) level 5 with second-digit (liquid) level 1.
Detailed comparison
The stronger rating on each row is highlighted in emerald.
Solid protection (first digit)
IP66
6 — Dust-Tight
IP51
5 — Dust-Protected
Liquid protection (second digit)
IP66
6 — Powerful Water Jets (12.5 mm nozzle)
IP51
1 — Vertically Dripping Water
Dust-tight
IP66
Yes
IP51
Limited
Water-jet resistant
IP66
Yes
IP51
No
Submersible
IP66
No
IP51
No
Outdoor suitable
IP66
Yes
IP51
No
The exact difference (IP66 vs IP51)
Solid protection
IP66
Level 6 — Dust-Tight
IP51
Level 5 — Dust-Protected
IP66 provides "Dust-Tight" (level 6), while IP51 provides "Dust-Protected" (level 5). IP66 is 1 level higher.
Liquid protection
IP66
Level 6 — Powerful Water Jets (12.5 mm nozzle)
IP51
Level 1 — Vertically Dripping Water
IP66 handles 100 kPa (Powerful Water Jets (12.5 mm nozzle)), while IP51 handles 0.1 mm/min drip rate (Vertically Dripping Water). IP66 provides 5 levels more liquid protection.
NEMA equivalents
No direct NEMA equivalent.
Recommendation
IP66 offers higher overall protection than IP51. Choose IP66 for harsher environments; IP51 may suffice for milder conditions and can be more cost-effective.