# Parameters for Varistor SPICE model

Can someone explain to me what the "limit" command in the following SPICE model of a Varistor means? Also, what are v(4) and v(8)?

.SUBCKT MOV  1 2 PARAMS: T=1 C=1pF L=1nH a1=1 a2=0 a3=0 a4=0 a5=0 a6=100u a7=100u
E_non_lin   3 1     VALUE {T*(
a1+a2*(log10(limit(v(4),a7,1g))-3)
a3/limit(v(4)*.001,a7/1e3,1g)
+a4*exp(-log10(limit(v(4),a7,1g))+3)
+a5*exp(log10(limit(v(4),a7,1g))-3)
-(a1+a2*(log10(-limit(v(4),-1g,-a7))-3)
-a3/limit(v(4)*.001,-1g,-a7/1e3)
+a4*exp(-log10(-limit(v(4),-1g,-a7))+3)
+a5*exp(log10(-limit(v(4),-1g,-a7))-3))
+limit(v(4)/a7*v(8),-v(8),v(8)))}
L_series    5 6  {L}
H_H1        4 0  VH_H1 1k
VH_H1       5 7 0V
R_R2        0 4  1G
R_series    6 2  {a6}
V_V1        3 7  0V
E_x_zero    8 0     VALUE {a1+a2*(log10(a7/1e3))+a3/(a7/1e3)+a4*exp(-log10(a7/1e3))+a5*exp(log10(a7/1e3))}
R_x_zero    8 0  1G
C_parallel  1 5 {C}
.ENDS
*
.SUBCKT V571BA60 1 2 PARAMS: TOL=0
X1  1 2 MOV PARAMS: T={1+TOL/100} L=75nH C=4.5nF a1=1050.5 a2=52.58 a3=-1.056e-3 a4=0.8805 a5=11.65 a6=3.266e-3 a7=25e-3
.ENDS
*
.SUBCKT V661BA60 1 2 PARAMS: TOL=0
X1  1 2 MOV PARAMS: T={1+TOL/100} L=75nH C=4nF a1=1212.2 a2=60.67 a3=-1.219e-3 a4=1.016 a5=13.44 a6=3.768e-3 a7=25e-3
.ENDS
*


I have the SPICE model from this website https://www.littelfuse.com/technical-resources_old/spice-models/varistor-spice-models.aspx

limit is a function whose definition is given by this reference manual (for example):

LIMIT(x,min,max)
result is min if x < min, max if x > max, and x otherwise


The documentation for your simulator should have similar information.

v(4) and v(8) are node voltages for nodes 4 and 8 in your .SUBCKT:

H_H1        4 0  VH_H1 1k
R_x_zero    8 0  1G